Drive device, in particular for the locking unit, the injection unit or the ejector of an injection-moulding machine for plastics

ABSTRACT

The invention relates to a drive device, which is used in particular for the locking unit, the injection unit, or the ejector of an injection-moulding machine for plastics and which has a drive element that can be axially displaced by an electromotor and a hydraulic unit that can be displaced in the same direction as the drive element by being entrained by the latter. The hydraulic unit is a power-transmission element comprising two pistons which can be displaced in relation to one another and have working surfaces of different dimensions. Said hydraulic unit is also an intermediate element, which together with the pistons encloses a pressure chamber that is filled with a hydraulic fluid, when the small piston with the smaller working surface is mechanically connected to the drive element, when the entire hydraulic unit is displaced for a control movement and when the intermediate element is locked to prevent it from being displaced in relation to a fixed frame, in order to enable the larger piston with the larger working surface to exert a great force.

[0001] The invention relates to a drive device which is to be used inparticular for the closing unit or the injection unit or the ejectors ofan injection molding machine for plastics and which has the features ofthe preamble of patent claim 1.

[0002] Inside the closing unit of an injection molding machine forplastics, the drive device moves the movable platen of the machine. Sucha drive device has to fulfill two important different requirements.Firstly, it is to move the platen as quickly as possible for closing andopening the mold, so that the cycle time for the production of a moldingcan be kept short. Secondly, it is to be able to lock the platen andthus the entire mold against the high injection pressure with highforce. On the one hand, therefore, regulating movements are to beperformed at high speed; on the other hand, high forces are to beexerted without substantial movement. Such requirements, apart from atthe closing unit, may also arise at the ejectors or the injection unitof an injection molding machine for plastics. For example, during theinjection of plastic into the mold, the plasticizing screw is moved atrelatively high speed in the direction of the mold until the mold iscompletely filled with plastic. If the plastic melt located in the moldis subsequently subjected to a “dwell pressure”, the drive has to applya high force without substantial movement of the plasticizing screw.

[0003] U.S. Pat. No. 4,030,299 discloses a purely hydraulic drive forthe movable platen of an injection molding machine for plastics, thishydraulic drive also containing a hydraulic power transmission means.The latter has a movable piston of small effective area, a furthermovable piston of large effective area and a cylinder which togetherwith the pistons encloses a pressure space filled with a pressure fluid.The cylinder is arranged in a fixed position on the frame of theinjection molding machine. In addition, the drive includes hydrauliccylinders which move the movable platen for closing and opening themold. In the opened state of the mold, the volume of the pressure spaceof the hydraulic power transmission means is minimal. If the movableplaten is now moved by the hydraulic cylinders for closing the mold, thelarge piston of the hydraulic power transmission means is carried along,in the course of which the volume of the pressure space of the hydraulicpower transmission means is increased and pressure medium flows from areservoir via a contraction valve into the pressure space. The smallpiston of the hydraulic power transmission means is subsequently movedinto the pressure space and thereby produces a high pressure whichproduces a high closing force via the large effective area of the largepiston. The small piston is moved hydraulically by the feeding ofpressure fluid. Thus, in the drive device according to U.S. Pat. No.4,030,299, there are various hydraulic drive components for theregulating movement of the movable platen and for exerting a high force.During the regulating movements of the platen, a large amount ofpressure fluid flows back and forth between the pressure space and thereservoir, a factor which makes correspondingly large valves and fluidpassages necessary.

[0004] A drive device having the features of the preamble of patentclaim 1 has been disclosed by DE 41 11 594 A1. In this drive device, ahydraulic cylinder having a large effective area is firmly connected tothe movable platen. The unit comprising movable platen and hydrauliccylinder can be moved by an electric motor via a drive mechanism, whichcomprises a stroke spindle and a spindle nut, in order to open and closethe mold quickly. The high closing force is applied by the admission ofpressure to the hydraulic cylinder movable with the platen. In theprocess, the entire reaction force is dissipated to the machine framevia the spindle and the spindle nut. The injection molding machine forplastics according to DE 41 11 594 A1, apart from being equipped withthe components of the electric drive, is also equipped with a completehydraulic system including oil reservoir, pump, valves and hydrauliccylinder.

[0005] The object of the invention is to develop a drive device whichhas the features of the preamble of patent claim 1 in such a way that aquick regulating movement is possible with little outlay on the one handand a large force effect can also be achieved on the other hand.

[0006] The set object is achieved by the fact that, according to theinvention, the drive device having the features of the preamble also hasthe features of the characterizing part of patent claim 1. In such adrive device, a hydraulic power transmission means is therefore used inwhose pressure space, at least during the regulating movement and thesubsequent exerting of a high force, a certain volume of a pressurefluid is trapped, if volumetric changes on account of a pressure changeare disregarded. Other hydraulic components are in principle notrequired for a drive device according to the invention. According to theinvention, the small piston of the hydraulic power transmission means ismechanically connected to the drive element, which can be moved axiallyby the electric motor. Furthermore, according to the invention, thehydraulic unit can be moved as an entity for the regulating movement ofan element to be driven, as a result of which the speed of the largepiston mechanically coupled to the element to be driven is equal to thehigh speed of the drive element axially moved by the electric motor. Inorder to be able to exert a high force, the intermediate part of thehydraulic power transmission means is locked against a displacementrelative to a fixed frame, so that, by further movement of the smallpiston by a relatively small amount of travel, a high pressure can bebuilt up in the pressure space of the power transmission means, and thishigh pressure produces a high force at the large effective area of thelarge piston. In this case, only a proportion of the force correspondingto the effective area of the small piston is to be absorbed via thedrive element.

[0007] According to patent claim 2, in order to be able to move thehydraulic unit as an entity, there is preferably a coupling device withwhich the intermediate part and the large piston of the hydraulic unit,during the regulating movement, are coupled to one another in a fixedposition.

[0008] According to patent claim 3, in an especially advantageousmanner, the coupling device comprises a spring which is secured inposition between the large piston and the intermediate part. When thehydraulic power transmission means comes into effect, said springcontinues to be compressed for a short length of travel, so that noadditional actuator is necessary for releasing the coupling between thelarge piston and the intermediate part of the power transmission means.In a configuration according to patent claim 4, the hydraulic unit,during the regulating movement, directly follows the small piston, sincethe spring does not first have to be loaded to a greater extent by apressure build-up in the pressure space in order to be able to transmitthe force required for the regulating movement. In a configurationaccording to patent claim 5, a short space-saving type of constructionof the hydraulic unit is possible, since the space required axially foraccommodating the spring can also be used in another way.

[0009] Patent claims 6 to 8 relate to constructional configurations ofthe hydraulic power transmission means which are likewise advantageousespecially with regard to a compact type of construction.

[0010] For good guidance of the large piston, it is advantageous if alarge guidance length is available. This is achieved by theconfiguration according to patent claim 9. In this case, the combinationof the configurations according to patent claims 5 and 9 is especiallyadvantageous, in which combination the guidance section is alsoavailable for accommodating the spring of the coupling device.

[0011] The coupling by a spring constitutes a frictional connectionbetween the intermediate part and the large piston, it being possiblefor this coupling to be released by applying a force which is above alimit force. However, it may also be favorable in certain cases if,according to patent claim 10, the intermediate part and the large pistonare coupled to one another in a positive-locking manner by the couplingdevice, it then being possible for the coupling device to be released byan actuator.

[0012] According to patent claim 11, in order to be able to move thehydraulic unit as an entity, a coupling device may also be providedbetween the drive element which can be moved by the electric motor orbetween the small piston and the intermediate part of the hydraulicunit, this coupling device being released when a high force is to beexerted and to this end the small piston is to plunge further into thepressure space. The coupling device is preferably a clutch, so that,during the locking movement, the drive part is not additionally loadedby the force required for overcoming the friction of a friction clutchand high accelerations of the hydraulic unit are also possible. In sucha construction, in principle no highly preloaded spring arranged betweenthe large piston and the intermediate part is required for the sequenceof movement. However, as specified in patent claim 12, a springpreloaded to a small extent and arranged in such a way is advantageous,since this spring can produce a certain preloading pressure at a levelof, for example, 5 bar in the pressure space and the latter can therebybe effectively vented.

[0013] In an especially preferred manner, however, a coupling device isprovided between the drive element or the small piston, on the one hand,and the large piston of the hydraulic unit, on the other hand, withwhich coupling device the large piston and the small piston are coupleddirectly to one another in a fixed position for a regulating movementand which is released when a high force is to be exerted and to this endthe small piston is to plunge further into the pressure space. Accordingto patent claim 14, the intermediate part is advantageously carriedalong by the large piston via a spring during the regulating movement.Here, too, the coupling device is preferably a clutch, in particular anelectromagnetic clutch. The latter preferably acts in the axialdirection, that is to say in the direction of movement of the powertransmission means.

[0014] According to patent claim 16, the coupling device between thedrive element or the small piston, on the one hand, and the intermediatepart or the large piston, on the other hand, is preferably a hydraulicclutch. In this case, pressure fluid, during the regulating movement, istrapped in a space between the two parts coupled to one another. Adisplacement of pressure fluid from the space is allowed in order to beable to move the two parts relative to one another.

[0015] According to patent claim 17, the coupling device between thedrive element or the small piston, on the one hand, and the intermediatepart or the large piston, on the other hand, is an in particularhydraulic slip clutch, that is to say a clutch in which a movement canbe transmitted via a trapped fluid volume up to a certain limit force.An advantage of such a clutch is its automatic mode of operation.Advantageous configurations of a hydraulic slip clutch can be found inpatent claims 18 to 20.

[0016] According to patent claim 21, a coupling device between the smallpiston and the large piston is preferably located in a cavity (clutchspace) of the large piston, into which cavity the small piston extends.The effective area of the small piston for the power transmission,according to patent claim 22, may be located in a blind hole which islocated on the other side of the cavity and from which there then has tobe a fluidic connection to a space at a large effective area of thelarge piston, or, according to patent claim 23, may be formed in asimple manner by a step of the small piston and be located in thepressure space in front of the cavity of the large piston.

[0017] According to patent claim 24, the locking of the intermediatepart of the hydraulic power transmission means relative to a fixedframe, this locking being provided for building up a high force, ispreferably effected by friction grip, since the intermediate part canthen be locked at any desired point without special provisions and nosetting work is required when changing the mold and during anaccompanying change in the closing travel. According to patent claim 25,for producing the friction grip, pressure is applied hydraulically toone of the two friction-grip partners. This pressure may be the pressureprevailing in the pressure space between the two pistons, in which casethere then has to be a fluidic connection between the pressure space andan admission space at the friction-grip partner. In this case, theclamping force is therefore applied by the electric motor, so that nofurther actuator is necessary. However, the intermediate part mustinitially be held in a fixed position until a pressure required for theclamping has built up in the pressure space. This may be effected by thespring secured in place between the large piston and the intermediatepart if it is preloaded to an appropriately high degree.

[0018] However, the pressure in the pressure space and thus also afriction grip only build up when the machine component to be moved hasbeen moved up to a stop. If, according to patent claim 27, a pressurecan be built up in the admission space at the one friction-grip partnerby feeding external pressure medium, that is to say pressure medium froma hydraulic circuit provided for producing the friction grip, theintermediate part can be locked at any point irrespective of theposition of the machine component. This is especially favorable for theproduction of moldings by “injection-compression molding”, in which amolding is first of all injection-molded with the mold halves notcompletely closed and is then compressed by closing the mold halves. Ifprovision is made for applying pressure to the one friction-grip partnerby feeding external pressure medium, this friction-grip partner ispreferably arranged in an axially fixed position on the machine frame,so that, when the individual hydraulic components of the hydrauliccircuit are fastened to the frame, pressure medium does not have to flowback and forth, for example, via a flexible hose between the hydraulicunit and the hydraulic components. The fastening of the hydrauliccomponents to the frame instead of a fastening to the hydraulic unit hasthe advantage that the mass to be accelerated and braked and thus theenergy input are lower.

[0019] According to patent claim 30, in an especially advantageousmanner, the friction grip is made possible by the intermediate part ofthe hydraulic unit having a tube section which can be elasticallyextended radially outward by internal pressure for producing a frictiongrip between the intermediate part and a wall of the bore of the fixedmachine frame. This elastically extensible tube section may even beguided with slight play in the bore. At a low internal pressure, it caneasily be displaced in the bore; at a high pressure, it becomes clampedand can transmit axial forces. To transmit such an axial force, arelatively large wall thickness is necessary, as a result of which ahigh pressure is necessary for deformation on the one hand and highstress occurs in the tube section on the other hand. It thereforeappears to be especially favorable if, according to patent claim 31,individual, radially movable brake rods are arranged around a thin,elastically extensible tube section, these brake rods lying axially withslight play between stops of the intermediate part. The brake rods maybe provided with a brake lining on the outer surface. If internalpressure is now applied to the tube section, it deforms and presses thebrake rods against the wall of the bore. Due to a high axial rigidity ofthe brake rods, high axial forces can already be transmitted at a lowdeformation pressure.

[0020] The configuration according to patent claim 35 appears to beespecially advantageous, according to which the intermediate part has adimensionally stable inner tube section, in which the large piston isguided in a sealed-off manner, and an outer tube section which surroundsthe inner tube section while forming a clearance space, pressure can beapplied to the clearance space, and the outer tube section can beelastically extended radially outward by pressure applied in theclearance space. In this case, compared with a construction according topatent claim 34, according to which that tube section of theintermediate part which guides the large piston is extensible, threedifferent things are achieved. Firstly, the clamping radius and thusalso the clamping force can be predetermined independently of thediameter of the large piston. Secondly, the clamping surface does notdepend on the relative position of intermediate part and large piston.In addition, the sealing of the pressure space between large piston andintermediate part is not affected.

[0021] In a construction according to patent claim 37, the outer,extensible tube section may be very thin without it giving way to theinside when its outer side is being machined, a factor which wouldentail inaccuracies in the external size of the hydraulic unit.

[0022] At high closing forces of, for example, 1000 kN, the productionof a friction grip between the intermediate part of the hydraulic unitand the frame according to patent claim 38 with interlocking sheet metalstacks at the intermediate part and at the frame, which sheet metalstacks can be compressed by an external force, appears to ensureespecially high operability of the drive device.

[0023] According to patent claims 39 to 46, the locking of theintermediate part is also possible by wedges.

[0024] According to patent claim 47, the intermediate part can also belocked hydraulically. Accordingly, the intermediate part can be lockedrelative to the fixed frame by trapping a pressure fluid volume locatedin a second pressure space. The volume of the pressure space changeswhen the intermediate part is moved. The pressure space can be connectedto a supply reservoir for the pressure fluid and can be shut off fromthe supply reservoir by a valve arrangement. The pressure space isarranged in a simple manner according to patent claim 48, in which casea cross section of similar size to the cross section of the firstpressure space can readily be obtained, so that the pressure in thesecond pressure space is in each case approximately as high as thepressure in the first pressure space.

[0025] Finally, it is also possible, according to patent claim 49, tolock the intermediate part by positive locking with the fixed frame.Patent claims 50 to 52 specify the way in which such positive lockingmay be advantageously configured.

[0026] If the intermediate part is locked by the radial engagement oflocking elements, a plurality of locking elements distributed around theperiphery are advantageous, which each have to be moved radially and forwhich axial adjustability is advantageous. Overall, therefore, themechanical outlay is relatively high. Locking of the intermediate partby an axial stop which can be moved in accordance with the regulatingmovement of the intermediate part appears to be more favorable. In thiscase, the force chain for axially supporting the intermediate partcomprises a self-locking screw spindle. It is possible, according topatent claim 54, for the stop to be capable of being moved by the sameelectric motor with which the drive element can also be moved or,according to patent claim 57, to allow said stop to be moved by a secondelectric motor. According to patent claim 58, the stop can be movedaxially after and ahead of the intermediate part in its direction ofmovement via a force chain in which the self-locking screw drive islocated. During the regulating movement, there is advantageously aslight distance of up to five tenths of a mm between the stop and theintermediate part, so that the stop is freely movable and the screwdrive is scarcely loaded and, on the other hand, the intermediate partcan be immediately supported without substantial travel to the rear.According to patent claim 59, the stop may also be formed by arotationally drivable part of the screw drive, this part meshingdirectly with a section, provided with a thread, of the intermediatepart. Here, the screw drive may be provided with appropriate play, sothat it is still subjected to low loading during the regulatingmovement.

[0027] According to patent claim 60, in order to prevent excessiveheating of the pressure fluid, cooling passages in which water flows maylead through the hydraulic unit and in particular the pressure space.

[0028] According to patent claim 61, the electric motor for moving thedrive element may be an electric linear motor, so that a screw spindleand a spindle nut for converting the rotational movement of the rotor ofan electric motor into a linear movement are not necessary.

[0029] An especially preferred construction is also contained in patentclaim 62, according to which the small piston of the hydraulic unit isformed as a hollow piston, and the screw spindle of a screw driveserving to move the small piston, which screw spindle can berotationally driven by the electric motor and is arranged in an axiallyfixed position, is accommodated by the hollow small piston. The smallpiston comprises a spindle nut which is in engagement with the screwspindle over the entire stroke and is locked against rotation. In thisembodiment, the space which is required by the hydraulic unit in thedirection of movement can also be used for the screw spindle, so that adrive device of especially short construction can be realized.

[0030] In principle, it is conceivable to keep the small piston closedon one side, in which case an end area on an end part of the smallpiston, this end part possibly being stepped in cross section relativeto the rest of the small piston, or also an annular area on an outerstep of the small piston may be the effective area. In this case, thesmall piston could also plunge into the large piston, formed as a hollowpiston, in order to be able to accommodate as long a piece of the screwspindle as possible. However, according to patent claim 63, the largepiston is preferably formed as a hollow piston, and the small piston ispreferably hollow throughout and is preferably formed as a steppedpiston with a section of larger outside diameter, with which it entersthe pressure space in a sealed-off manner, and with a section of smalleroutside diameter, with which it enters the hollow large piston. Thedifferential area between the two sections is the smaller effectivearea. The small piston may now be relatively short. Provided the screwspindle projects beyond the small piston, it is accommodated by thelarge piston.

[0031] In a construction of the small piston as a stepped piston whichsurrounds the screw spindle and is assembled with the spindle nut, theconstruction can be very complicated and the assembly difficult. Incontrast, in the especially expedient configuration according to patentclaim 66, the small piston is formed by a plurality of little pistonswhich are arranged outside the axis of the hydraulic unit, are supportedaxially on the spindle nut and plunge into holes of the cylinder base.Guidance of the little pistons in the cylinder base free of jamming ispermitted owing to the fact that the little pistons are only supportedaxially on the spindle nut. According to patent claim 67, the pressurespace can be sealed off independently of the spindle nut if the largepiston plunges with an annular section between two axial walls of thecylinder of the hydraulic unit. According to patent claim 68, for ashort type of construction, the spindle nut plunges into the centralpassage of the cylinder base.

[0032] The temperature of the pressure fluid located in the pressurespace depends on the operating period, the cycle times and the ambienttemperature. According to patent claim 69, in order to compensate for avolumetric change accompanying a temperature change, the pressure spaceof the hydraulic unit can be connected to a hydraulic accumulator.During the build-up of a high pressure in the pressure space, it is notto be possible for any pressure fluid to be displaced into the hydraulicaccumulator, since otherwise large travel of the small piston would benecessary. In order to avoid this, the hydraulic accumulator, accordingto patent claim 70, can be formed in such a way that its maximumcapacity is already reached at a low pressure within the range of, forexample, 5 to 10 bar. However, it is also conceivable, according topatent claim 71, for a valve to be arranged in the fluid connectionbetween the hydraulic accumulator and the pressure space, with whichvalve the fluid connection can be shut off. The valve may be operated asa function of the pressure in the pressure space or as a function of theposition of the hydraulic unit, possibly together with anelectromagnetically actuable clutch.

[0033] An especially short type of construction of a drive deviceaccording to the invention is obtained according to patent claim 73 bythe large piston being formed as a diaphragm piston with a diaphragm.According to patent claim 74, the diaphragm is advantageously of elasticconstruction and at the same time constitutes the coupling device withwhich the intermediate part and the large piston are coupled to oneanother in a fixed position for the regulating movement.

[0034] According to patent claim 75, the diaphragm is preferablyfastened at its outer margin to the intermediate part of the hydraulicunit and is provided centrally for fastening to the part to be moved. Nosliding movement takes place between piston and intermediate part. Thepressure space can be sealed off to the outside especially effectively.In this case, an especially effective seal is obtained by aconfiguration according to patent claim 76, since no parts are movedrelative to one another at the sealing points. A type of bellows is usedfor the sealing, provision being made to ensure that the bellows doesnot migrate into any gap and that it is not damaged and ultimatelydestroyed as a result.

[0035] Sometimes a force which is of similar magnitude to the lockingforce is required for opening the mold on an injection molding machinefor plastics. In the case of such a requirement, the power transmissionmeans of a drive device according to the invention, according to patentclaim 77, is advantageously constructed so as to be double-acting, inwhich case at least the large piston is constructed so as to bedouble-acting. Two different small pistons may be used. In principle,however, one small piston is sufficient, this small piston, the largepiston and the intermediate part together enclosing two closed pressurespaces which are separate from one another, are filled with a pressurefluid and are located on opposite sides of the pistons. In quite generalterms, not only may travel be executed very quickly in oppositedirections but a high force may also be exerted with such a drivedevice.

[0036] A cycle, for example, may appear as follows: travel rapidly inthe one direction, lock in the same direction, travel rapidly in theopposite direction, lock in the opposite direction.

[0037] In principle, it is possible to form the two pistons asdifferential pistons, in which case, depending on which piston areasdefine a pressure space, power transmission ratios which are quitedifferent in the two opposite directions may be obtained. However, thetwo pistons are preferably synchronous pistons, so that the same ratiosprevail in the opposite directions.

[0038] Advantageous configurations of a double-acting drive deviceaccording to the invention can be found in patent claims 79 to 82.

[0039] So that the screw spindle does not perform any wobbling movementwith its one end, it is expediently rotatably mounted at the end.However, if the screw spindle is axially fixed and the bearing part isthe large piston which moves relative to the screw spindle, the axialmisalignment between screw spindle and bearing part may change during aworking cycle, so that, in the case of a radially fixed bearing, thescrew spindle would be subjected to high alternating bending forces andcould become sluggish. Provision is therefore made according to patentclaim 83 for the one end of the screw spindle to be mounted in a radialbearing which, if a radial force exceeds a limit force, is radiallyadjustable relative to a guide bush serving for the longitudinalguidance of the screw spindle.

[0040] According to patent claim 84, a drive device according to theinvention for closing and opening the mold on an injection moldingmachine for plastics is advantageously combined with a drive device foractuating an ejector or a plurality of ejectors.

[0041] If the coupling device between the small piston and the one otherpart of the power transmission means functions hydraulically, it isfavorable if, according to patent claim 85, the clutch space, for theregulating movement, can be connected to a charged high-pressureaccumulator. The pressure fluid in the clutch space, without movement ofthe small piston, can then already be prestressed to such a pressurethat the other part directly follows the movement of the small piston.According to patent claim 86, the clutch space, after the end of aregulating movement, is advantageously connected to a low-pressureaccumulator, that is to say a hydraulic accumulator with low pressure,so that, during the effectiveness of the power transmission, noadditional work has to be performed for the displacement of pressurefluid into the high-pressure accumulator. If the clutch space, during aworking cycle, is alternately connected to the high-pressure accumulatorand to the low-pressure accumulator or to a space relieved toward thelow-pressure accumulator during a period of a working cycle, in eachcase a small quantity of pressure fluid, on account of thecompressibility of the pressure fluid, passes from the high-pressureaccumulator into the low-pressure accumulator. In principle, it ispossible to pump this quantity back into the high-pressure accumulatoragain by a small hydraulic pump with separate drive motor and in thisway keep the pressures in the hydraulic accumulators at the desiredlevel. The outlay would probably be lower if, according to patent claim87, the small piston has a pump piston section which adjoins adisplacement chamber and by the reciprocal movement of which pressuremedium can be drawn from the low-pressure accumulator into thedisplacement chamber and can be displaced from the displacement chamberinto the high-pressure accumulator. The pressure medium is drawn in anddisplaced in an especially simple manner in each case via a check valve,as is usually the case in piston pumps. In this case, it certainlyappears possible for the pressure fluid quantity delivered by the pumppiston section to correspond exactly to the quantity entrained into thelow-pressure accumulator from the high-pressure accumulator on accountof the compressibility, but this is difficult to realize. Therefore, thedelivered quantity is made slightly larger than the entrained quantityand, according to patent claim 88, a spill valve is arranged between thehigh-pressure accumulator and the low-pressure accumulator, this spillvalve opening if the pressure difference between the two hydraulicaccumulators exceeds a certain magnitude.

[0042] If the power transmission means is constructed so as to bedouble-acting, the configuration according to patent claim 89 appearsespecially advantageous. The first piston section is not carried alongduring the pressure build-up in the one direction, so that the firstsmall pressure chamber is not further enlarged in its volume and novacuum arises therein even without special measures. According to patentclaim 90, the second small pressure chamber does not adjoin the firstpiston section of the small piston, so that the movement of the firstpiston section away from the stop does not contribute to the change inthe volume of the second small pressure chamber, but rather itsvolumetric change is determined solely by the effective area of thesecond piston section and remains small if the effective area iscorrespondingly small.

[0043] By the spring which is present according to patent claim 91, aslip clutch between the two piston sections of the small piston orbetween the drive element and the first piston section in the onedirection is created in a simple manner.

[0044] Several exemplary embodiments of a drive device according to theinvention are shown in the drawings. The invention will now be explainedin more detail with reference to these drawings, in which:

[0045]FIG. 1 shows a first exemplary embodiment in which the driveelement is driven by a rotary electric motor via a stroke spindle, andthe intermediate part of the power transmission means can be locked byradial widening by friction grip,

[0046]FIG. 1a shows a variant of the first exemplary embodiment, arestoring plate acting on the large piston and not on the intermediatepart of the power transmission means,

[0047]FIG. 2 shows a second exemplary embodiment in which theintermediate part of the power transmission means can be locked bypivotable locking bars by positive locking,

[0048]FIG. 3 shows a third exemplary embodiment in which theintermediate part of the power transmission means can be locked by atype of multiple-disk brake again by friction grip,

[0049]FIG. 4 shows a fourth exemplary embodiment in which the pressurefluid is cooled by a cooling passage,

[0050]FIG. 5 shows a fifth exemplary embodiment which is largelyidentical to the first exemplary embodiment, but in which a clutch islocated between the drive element and the intermediate part of the powertransmission means,

[0051]FIG. 6 shows a sixth exemplary embodiment in which theintermediate part, in addition to a guide tube for the large piston, hasa clamping tube which can be radially widened on a larger diameter,

[0052]FIG. 7 shows a seventh exemplary embodiment, again with a clampingtube which is separate from the guide tube and which is very thincompared with the clamping tube of the sixth exemplary embodiment andrests on the guide tube in the relieved state,

[0053]FIG. 8 shows an eighth exemplary embodiment in which theintermediate part of the power transmission means can be clamped bywedges in a bore of a machine part,

[0054]FIG. 9 shows a ninth exemplary embodiment in which theintermediate part of the power transmission means can be clamped bywedges on spars of a machine, it being possible for the pressure in thepressure space to be applied to the wedges,

[0055]FIG. 10 shows a tenth exemplary embodiment in which theintermediate part of the power transmission means, as in the ninthexemplary embodiment, can be clamped by wedges on spars of a machine,but in which spring pressure can be applied to the wedges,

[0056]FIG. 11 shows an eleventh exemplary embodiment in which theintermediate part of the power transmission means can be hydraulicallylocked directly by a trapped pressure fluid volume,

[0057]FIG. 11a shows a variant of the eleventh exemplary embodiment ofthe pressure-medium reservoir,

[0058]FIG. 12 shows a twelfth exemplary embodiment in which theintermediate part of the power transmission means can be locked by anaxial stop which follows the intermediate part,

[0059]FIG. 13 shows a thirteenth exemplary embodiment in which, as inthe twelfth exemplary embodiment, the intermediate part of the powertransmission means can be locked by an axial stop which follows theintermediate part, it being possible for the stop to be moved by asecond electric motor,

[0060]FIG. 14 shows a fourteenth exemplary embodiment in which theintermediate part can be locked by a threaded part which can be rotatedby a second electric motor,

[0061]FIG. 15 shows a fifteenth exemplary embodiment in which guide tubeand clamping tube are again separate and in which, for controlling thepower transmission means, the small piston and the large piston arecoupled to one another via a hydraulic slip clutch,

[0062]FIG. 16 shows a sixteenth exemplary embodiment in which theclamping tube is surrounded by individual brake rods and in which, forcontrolling the power transmission means, the small piston and the largepiston can be coupled to one another via an electromagnetic clutch,

[0063]FIG. 17 shows a view in the axial direction of the clamping tubeand the brake rods surrounding it from FIG. 16,

[0064]FIG. 18 shows a cross section through an individual brake rod,

[0065]FIG. 19 shows a seventeenth exemplary embodiment in which theintermediate part of the power transmission means can be locked viabrake shoes which are held on the frame and to which external pressuremedium can be applied,

[0066]FIG. 20 shows an eighteenth exemplary embodiment which is ofsimilar construction to the sixteenth exemplary embodiment, but in whichan external pressure medium can be applied on the inside to the clampingtube, and

[0067]FIG. 21 shows a nineteenth exemplary embodiment in which both thesmall piston and the large piston of the hydraulic unit are formed ashollow pistons and accommodate the screw spindle, rotationally driven bythe electric motor, of a screw drive for moving the small piston,

[0068]FIG. 22 shows a twentieth exemplary embodiment which is of similarconstruction to the nineteenth exemplary embodiment, but in which thesmall piston is formed by a plurality of little pistons and in which thepressure space is connected to a piston accumulator, the capacity ofwhich is exhausted at low pressure,

[0069]FIG. 23 shows a special bearing arrangement of the one end of thescrew spindle from FIG. 22,

[0070]FIG. 24 shows a twenty-first exemplary embodiment which is ofsimilar construction to the sixteenth exemplary embodiment, but in whicha fluid connection between the pressure space and a hydraulicaccumulator can be controlled via a directional control valve,

[0071]FIG. 25 shows a twenty-second exemplary embodiment in which thesmall piston is formed by a plurality of little pistons and the largepiston is formed by a diaphragm piston,

[0072]FIG. 26 shows a twenty-third exemplary embodiment which has adouble-acting hydraulic power transmission means,

[0073]FIG. 27 shows a variant of the twentieth exemplary embodiment,this variant being additionally equipped with a drive device for anejector,

[0074]FIG. 28 shows a further variant of the twentieth exemplaryembodiment having a drive device for a plurality of ejectors,

[0075]FIG. 29 shows a view of the drive device for the ejector accordingto FIG. 28 in the axial direction,

[0076]FIG. 30 shows a further variant of the twentieth exemplaryembodiment having another drive device for a plurality of ejectors, and

[0077]FIG. 31 shows a section along line D-D from FIG. 30,

[0078]FIG. 32 shows the twenty-fourth exemplary embodiment, in which, asin the exemplary embodiment according to FIG. 15, the small piston andthe large piston can be hydraulically coupled to one another, and thesmall piston, as in the exemplary embodiment according to FIG. 16, hasan annular area as effective area for the power transmission,

[0079]FIG. 33 shows the twenty-fifth exemplary embodiment, in which thesmall piston can be hydraulically coupled to the intermediate part ofthe hydraulic unit,

[0080]FIG. 34 shows the twenty-sixth exemplary embodiment, in which thesmall piston can likewise be coupled to the intermediate part of thepower transmission means, and the power transmission means isconstructed so as to be double-acting,

[0081]FIG. 35 shows the twenty-seventh exemplary embodiment, which is ofsimilar construction to that according to FIG. 34, but in which theclutch space between the small piston and the intermediate part is atthe same time also a sectional space of a pressure space of the powertransmission means.

[0082] According to FIG. 1, an electric motor 11 and a hydraulic powertransmission means 12 of circular-cylindrical cross section on theoutside are accommodated by a stepped bore 9 of a machine frame 10. Ahousing 13 of the electric motor 11 is essentially composed of twobearing plates 14 and 15 and a housing shell 16. Sitting on the latteron the inside is the stator 17 of the electric motor. The rotor 18 ofthe electric motor sits on a hollow drive shaft 19 which is rotatablymounted in two rolling-contact bearings 20 held in the bearing plates 14and 15 and in which a ball groove thread 21 is formed on the inside.

[0083] Located inside the hollow drive shaft 19 is a stroke spindle 25which is locked against rotation and has a first section 26 whichconstitutes the actual stroke spindle and has a diameter which isapproximately equal to the inside diameter of the drive shaft 19 and isprovided on the outside with a ball groove thread 27. Located betweenthe latter and the ball groove thread 21 of the drive shaft 19 are balls28, via which the drive shaft 19 and the stroke spindle 25 are coupledto one another. The stroke spindle 25 has a second section 28 which hasa circular-cylindrical shape and is smaller in diameter than the firstsection 26. A restoring disk 29 is fastened to the free end of thesection 28.

[0084] The second section 28 of the stroke spindle 25 constitutes partof the hydraulic power transmission means 12. Specifically, it is thesmall piston with the smaller effective area and plunges into a pressurespace 35, filled with a hydraulic fluid, of the hydraulic powertransmission means 12. In addition, the latter has a large piston 36with a large effective area and also an intermediate part 37 which is atrest when the force transmission is being utilized and, in all theexemplary embodiments shown, is a cylinder accommodating the largepiston 36. In the exemplary embodiment according to FIG. 1, the cylinderis composed of a first end flange 38 with a central opening 39, thediameter of which corresponds to the diameter of the small piston 28 andthrough which the piston 28 enters the pressure space 35 in a sealed-offmanner. The restoring disk 29 is fastened inside the pressure space 35to the end face of the piston 28. A second end flange 40 of the cylinder37 likewise has a central opening 41. Its diameter is larger than thediameter of the opening 39 in the flange 38. A piston rod 42 of thelarge piston 36 is located in the opening 41. Extending between the twoflanges 38 and 40 and tightly connected to them is the tubular cylinderenvelope 43, which, except for two annular, inwardly directed widenedportions at its ends, these widened portions serving for fastening tothe flanges, is formed to be so thin-walled that it can be extendedelastically outward by an internal pressure. When the cylinder envelope43 is not extended, there is a slight clearance between the envelope andthe bore 9, which has a slightly larger diameter in the region of theelectric motor than in the region of the power transmission means 12.

[0085] The large piston 36 is essentially formed in two pieces and has apot-shaped outer part 44 with a base 45 and an envelope 46, whichextends from the base 45 at a radial distance from the cylinder envelope43 in the direction of the flange 40 of the cylinder 37 and has an outerflange 47 at its free end, at which outer flange 47 the large piston 36and cylinder 37 are guided on one another and sealed off from oneanother at a point 50. A further guide 49 between the piston 36 and thecylinder 37 is located in the region of the base 45. This guide 49 isinterrupted in sections, so that the space outside the envelope 46 ofthe pot 44 is freely connected to the space between the base 45 of thepot 44 and the flange 38. Furthermore, there are spacers 48 between thebase 45 and the flange 38 of the cylinder 37, so that the base 45 cannotbear flat against the flange 38 and there is a free connection of allthe clearance spaces between the flange 38 and the large piston 36,these clearance spaces forming the pressure space 35.

[0086] A central opening 55 in which the piston rod 42 is fastened islocated in the base 45 of the outer part 44 of the large piston 36. Thesmall piston 28 together with the restoring disk 29 can plunge into ablind hole 56, open toward said small piston 28, of the piston rod 42.

[0087] The outside diameter of the piston rod 42 is smaller than theinside diameter of the envelope 46 of the outer part 44, so that anannular groove 57 is produced in the piston 36, this annular groove 57being open toward the flange 40 of the cylinder 37 and accommodating ahelical compression spring 60 which is secured in position between thebase 45 of the piston 36 and the flange 40 of the cylinder 37 and thusloads these two parts in such a direction that the piston 36 bearsagainst the flange 38 of the cylinder 37 via the spacers 48. When saidpiston 36 comes to bear, the helical compression spring 60 is loaded insuch a way that it can transmit the force required for the regulatingmovement of the platen of an injection molding machine for plasticswithout increasing the preloading.

[0088] The pressure space 35 including the blind hole 56 is filled witha pressure fluid, to be precise with a silicone oil, which has goodthermal stability and ages substantially more slowly than a mineral oil.The space between the flange 40 and the piston 36 is connected to theatmosphere via holes in the flange 40.

[0089] In FIG. 1, the drive device is shown in a state in which the moldof an injection molding machine for plastics is completely open. Therestoring plate 29 of the small piston 28 and the large piston 36 bearagainst the flange 38 of the cylinder 37. The pressure in the pressurespace 35 is thus lower than the pressure equivalent to the helicalcompression spring 60. However, it is higher than the pressure which isnecessary in order to transmit the force required for the regulatingmovement of the platen. If the mold is now to be closed, the electricmotor is activated in such a way that its rotor rotates in a directionin which an axial movement of the stroke spindle 25 is effected to theright as viewed according to FIG. 1. Since the pressure in the pressurespace 35 is sufficiently high, the large piston 36 immediately followsthe movement of the small piston 28 and also carries along the cylinder37 via the helical compression spring 60. Finally, the mold is closed,so that a high resistance counteracts the further movement of the largepiston 36. The stroke spindle continues to be moved, so that the smallpiston 28 plunges deeper into the pressure space 35. As a result, thepressure in the pressure space 35 increases, in the course of which thehelical compression spring 60, subjected to appropriately highpreloading, first of all prevents the cylinder 37 from giving way to theleft. Finally, by further pressure increase, the cylinder envelope 43 iswidened to such an extent that it abuts on the inside against the wallof the bore 9. As a result, the cylinder 37 is held in its position byclamping, that is by friction grip, even if this can no longer beeffected solely by the helical compression spring 60. The mold is nowlocked with a high closing force, which results from the product of thepressure in the pressure space 35 and the effective area of the largepiston 36 less the force of the helical compression spring 60. On theother hand, the reaction force on the stroke spindle 25 is determined bythe product of the pressure in the pressure space 35 and thesubstantially smaller effective area of the small piston 28. The loadingof the ball screw drive is therefore low.

[0090] To open the mold, the electric motor 11 is driven in the oppositedirection. The stroke spindle 25 travels to the left and finally, viathe restoring plate 29, the cylinder 37, the helical compression spring60 and the large piston 36, carries along the platen with the mold halffastened thereto.

[0091] In the embodiment shown in FIG. 1, the restoring plate 29 acts onthe flange 38 of the cylinder 37. It is also conceivable, according to avariant, shown in FIG. 1a, of the embodiment according to FIG. 1, forthe restoring plate 29 to engage behind a shoulder 30 on the piston 36and for the retraction of the platen by the stroke spindle 25 to takeplace directly via the large piston 36. In this case, it is advantageousthat the platen, during the closing of the mold, can be braked directlyvia the stroke spindle 25 and the large piston 36 and not via thehelical compression spring 60. According to FIG. 1a, the restoring plate29 has opposite flats. The shoulder 30 comprises only two oppositeindividual projections, between which the inside radius of the pistonrod 42 is equal to the radius of the blind hole 56. The gaps between thetwo projections are so large that the large piston 36 and the smallpiston 38 can be inserted one inside the other and be released from oneanother in a bayonet-like manner. Since the two pistons 28 and 36 arelocked against rotation in the ready-to-operate state, they cannot bereleased from one another. Via the flats on the restoring disk 29 andthe gaps between the projections 30, there is a free fluidic connectionbetween the blind hole 56 and the remaining parts of the pressure space35.

[0092] The exemplary embodiment shown in FIG. 2 essentially shows onlythe hydraulic unit 12. This hydraulic unit 12 again has a cylinder 37, alarge piston 36 and a small piston 28 with a restoring plate 29 whichengages behind an end flange 38 of the cylinder 37. The latter, in theexemplary embodiment according to FIG. 2, is only formed in two piecesand, in addition to the flange 38, has a dimensionally stable envelope63, to which the flange 38 is screwed and which, at a distance from theflange 38, has an inner shoulder 64, on which the helical compressionspring 60, also present in the second exemplary embodiment, is supportedand which serves as a travel limit for the large piston 36. Behind theinner shoulder 64, an annular groove 65 runs on the outside around theenvelope 63. The large piston 36 is constructed in a similar manner tothe same piston of the first embodiment and has a blind hole 56 which ispart of the pressure space 35, an annular groove 57 which accommodatesthe helical compression spring 60, and a piston rod 42 which movesfreely outward inside the shoulder 64. The space in which the helicalcompression spring 60 is located is connected to the atmosphere inexactly the same way as in the embodiment according to FIG. 1.

[0093] The cylinder 37 is axially guided in a ring 70 which, with anexternal thread 71, interacts with an internal thread of the machineframe 10. At one end, the ring 70, with a stop 72, overlaps the outsidediameter of the cylinder 37 toward the inside and thus limits the travelof the cylinder 37 in the one direction. In front of the stop 72, anannular groove 73 open to the inside is made in the ring 70. Running atequal angular distances from one another between the other end of thering 70 and the annular groove 73 are a plurality of axial holes 74,through which bolts 75 are inserted, of which each carries a lockingelement 76 at one end in the annular groove 73. The bolts 75 can beturned by acting on the other end. The bolts 75 can assume a rotaryposition in which the locking elements 76 do not engage in the groove 65of the cylinder 37. This is shown at the top in FIG. 2. The cylinder 37is then freely movable within its stroke range. If the cylinder 37 bearsagainst the stop 72 of the ring 70, the locking elements 76 can be swunginto the annular groove 65 by turning the bolts 75. The cylinder 37 ofthe hydraulic power transmission means 12 is then locked in a positivemanner against movement. The functioning of the exemplary embodimentaccording to FIG. 2 is the same as that of the exemplary embodimentaccording to FIG. 1. However, locking of the cylinder 37 is not nowpossible in every position. In order to bring the locking position ofthe cylinder 37 into conformity with a certain closing position of theplaten, the ring 70 is rotated in the machine frame 10 and as a resultthe stop 72 and the locking elements 72 are axially adjusted.

[0094] In the exemplary embodiment according to FIG. 3, the cylinder 37can again be locked by friction grip and thus in any desired position.In this case, however, the locking device, compared with the embodimentaccording to FIG. 1, is formed in such a way that very high reactionforces can be withstood. The locking device in this case comprises twostacks of metal sheets 77 and 78 and one or more actuators (not shown inany more detail). The two outermost metal sheets 77 are fastened to theouter surfaces of the cylinder 37 via screws 79, of which only one isshown in FIG. 3. The other metal sheets 77 are held on the cylinder byscrews 80 which run outside the cylinder 37 and also pass through thetwo outermost metal sheets, a spacer 81 being arranged in each casebetween two metal sheets. The stack of metal sheets 78 is firmlyconnected to the machine frame (not shown in any more detail) and heldtogether via screws 82, a spacer 81 also being arranged here in eachcase between two metal sheets. The two stacks of metal sheets interlockand can be pressed against one another by the actuators like the disksof a multiple-disk brake. In this way, frictional locking of thecylinder 37 even against high acting forces is also possible.

[0095] The embodiment according to FIG. 4, in which only one half of thehydraulic power transmission means of this embodiment is shown, largelycorresponds to that according to FIG. 1. The hydraulic powertransmission means 12 again has a small piston 28, which is axiallymovable by an electric motor via a spindle drive, a large piston 36 anda cylinder 37. The cylinder has a flange 38, a flange 40 and a cylinderenvelope 43 which can be widened by an internal pressure and pressedagainst a wall of the machine frame 10. A helical compression spring 60is again secured in position between piston 36 and cylinder 37, the sealbetween the cylinder envelope 43 and the piston 36 now being located infront of the piston-side end of the compression spring 60 and the powertransmission means accordingly being constructed to be longer than inthe embodiment according to FIG. 1. The space in which the compressionspring 60 is located is again connected to the atmosphere. The pressurespace 35 is filled with a pressure fluid. So that heat can be dissipatedfrom the latter, a cooling coil 85 through which cold water can beconducted leads through the pressure space 35.

[0096] The exemplary embodiment according to FIG. 5 is largelyconstructed like the exemplary embodiment according to FIG. 1 in itsvariant according to FIG. 1a. The same parts are therefore provided withthe same designations as in FIG. 1 without this being dealt with in moredetail here. Only the differences shall be considered below.

[0097] According to FIG. 5, the large piston of the fifth exemplaryembodiment is produced from a single piece.

[0098] Compared with the exemplary embodiment according to FIG. 1, thedistance between the electric motor 11 and the base 38 of the cylinder37 is increased. Accordingly, the second section 28 of the strokespindle 25 is lengthened. Arranged in the space created between theelectric motor 11 and the cylinder 37 is a clutch 85, via which thestroke spindle 25 can be coupled directly to the cylinder 37. The clutchis actuated electromagnetically, an electric winding 86 beingaccommodated in an axially open groove of the base 38 of the cylinder37. When the winding is not energized, a flat armature 87 is held at adistance from the base 38 by springs 88. A plurality of elasticallydeformable hooks 89 are fastened to the base 38 around the section 28 ofthe stroke spindle 25, these hooks 89 being bent inward by a movement ofthe flat armature 87 toward the base 38 and engaging in annular grooves90 of the stroke spindle 25. The clutch thus comes into effect byenergizing the winding 86.

[0099] In the exemplary embodiment according to FIG. 5, the clutch 85enables the hydraulic unit 12 and the movable platen, fastened to thepiston 36, of an injection molding machine for plastics to beaccelerated very rapidly by a very high force which exceeds the forcewhich can be transmitted by the spring 60. When the mold is closed, theclutch 85 is released. The stroke spindle 25 continues to be moved, sothat the small piston 28 plunges deeper into the pressure space 35. As aresult, the pressure in the pressure space 35 increases, in the courseof which the helical compression spring 60, which is preloaded to thesame extent as in the first exemplary embodiment, first of all preventsthe cylinder 37 from giving way to the left. Finally, by furtherpressure increase, the cylinder envelope 43 is widened to such an extentthat it abuts on the inside against the wall of the bore 9.

[0100] To open the mold, the electric motor 11 is driven in the oppositedirection and carries along the platen directly via the restoring plate29 and the large piston 36 without a spring in between.

[0101] If, in a variant (not shown) of the fifth exemplary embodiment,the cylinder 37 is not locked by being acted upon by the pressureprevailing in the pressure space 35 but, independently thereof, islocked mechanically or hydraulically, the helical spring is notnecessary. However, it is The same pressure as in the pressure space 35thus prevails in the clearance space 96 and therefore on the inside ofthe outer tube 92. When a pressure is therefore built up in the pressurespace 35 by the small piston 28 plunging into the pressure space 35,pressure is also applied outward to the outer tube 92 and the latterclamps the cylinder 37 in place in the bore 9 (omitted in FIG. 6). Thesize of the clamping surface can thus now be selected independently ofthe size of the large piston 36. In addition, the guidance and sealingof the large piston 36 at the cylinder 37 is not influenced by theclamping. This is because the tube 94 is so robust that it is scarcelydeformed inward by the pressure acting on it from the outside.

[0102] There is also a helical compression spring 60 in the embodimentaccording to FIG. 6, via which helical compression spring 60 thecylinder 37 can be carried along by the large piston 36, and, after theclosing of the mold, the cylinder 37 can be held until a pressure, bywhich the cylinder 37 is clamped, has built up due to the piston 28continuing to plunge into the pressure space 35.

[0103] Also in the exemplary embodiment according to FIG. 7, theclamping diameter for the cylinder 37 of the hydraulic unit 12 isdifferent from the guidance and sealing diameter of the piston 36. Thelatter, as in the exemplary embodiments according to FIGS. 1 and 5, isagain formed in two pieces with an outer part 44 and an inner part withpiston rod 42. At its end facing the base 38 of the cylinder 37, theinner part has an inner shoulder 101, behind which a restoring disk 29on the small piston 28 engages. The piston 36 is now continuously hollowcentrally, so that the restoring disk 29 can be fastened to the smallpiston 28 from the free end of the piston rod 42. In this case, it ispushed over a threaded stem 102 of the piston 28 up to an outer shoulderand is secured by a nut 103. From the free end, the piston rod 42 has aninternal thread, into which a connecting piece 104 for the movableplaten is screwed in a sealed-off manner.

[0104] As in the embodiments according to FIGS. 1 and 5, the cylinder 37has a base 38, a flange 40 and an inner tube 94 which runs between thesetwo parts and which has a large wall thickness and is accordinglydimensionally stable. The large piston 36 is guided axially in the tube94 by means of the outer part 44 at two points which are at aconsiderable distance from one another and correspond to the points 49and 50 of the exemplary embodiments according to FIGS. 1 and 5. Theclearance space axially between these two points 49 and 50 and radiallybetween the piston 36 and the cylinder 37, unlike in the exemplaryembodiments according to FIGS. 1 and 5, is not filled with pressurefluid but is now connected via radial holes 104 in the outer part 44 ofthe piston 36 to the annular groove 57 accommodating the helicalcompression spring 60 and thus to the atmosphere. Accordingly, theguidance of the piston 36 at the point 50 need not be tight. On theother hand, there must be a sound seal at the point 49 and at thepassage of the piston 28 through the base 38 of the cylinder 37. In theexemplary embodiment according to FIG. 7, therefore, sealing rings 106which are permanent magnets are used at the point 49 and between thepiston 28 and the base 38 of the cylinder 37. Located in the pressurespace 35 is a pressure fluid which is magnetorheological. Such a fluidhas a viscosity which depends on the strength of a magnetic fieldpassing through it. The stronger the magnetic field, the higher theviscosity. Thus the pressure fluid used in the exemplary embodimentaccording to FIG. 7 in the region of the sealing rings 106 is highlyviscous, so that an extremely effective seal is possible.

[0105] Made in the outside of the tube 94 of the cylinder 37 is a spiralgroove 97 which is fluidically connected to the pressure space 35 via aplurality of radial holes 98 passing through the tube 94. Compared withthe exemplary embodiment according to FIG. 6, the tube 94 is surroundedby a very thin-walled outer tube 92 which bears against the inner tube94 when there is absence of force between the individual turns of thespiral groove 97. The outer tube 92 therefore does not give way inwardlyduring the final machining of its outside, e.g. by grinding, so that thehydraulic unit 12 can be produced with an accurate external dimensionand there is little risk of jamming in the bore 9 during the regulatingmovement. The tube 92 bears with a certain prestress against the tube94, so that the pressure which occurs in the pressure space 35 duringthe regulating movement and which is thus also applied in the spiralgroove 97 still cannot widen the tube 92 outward.

[0106] In FIG. 7, the hydraulic unit is shown in a state in which themold of an injection molding machine for plastics is completely open.The restoring plate 29 of the small piston 28 bears against the largepiston 36 and the latter in turn bears against the cylinder 37. If themold is now to be closed, the small piston 28 is moved to the right inthe view according to FIG. 7. If the pressure in the pressure space 35was already sufficiently high at the start, the large piston 36 directlyfollows the movement of the small piston 28 and also carries along thecylinder 37 via the helical compression spring 60. In the process, thepressure in the pressure space 35, which is also applied in the spiralgroove 97, is not yet sufficient in order to widen the outer tube 92.Finally, if the mold is closed, a high resistance opposes the furthermovement of the large piston 36 and the pressure in the pressure space35 increases as the small piston 28 plunges deeper into the pressurespace 35, of which the cavity in the piston 36 is a part. First of all,the helical compression spring 60, subjected to appropriately highpreloading, prevents the cylinder 37 from giving way to the left.Finally, by further pressure increase, the outer tube 92 is widened, sothat it abuts on the inside against the wall of the bore 9. The cylinder37 is then held by clamping in the bore 9, and, by further movement ofthe small piston 28, the pressure in the pressure space 35 can befurther increased in order to exert a high locking force for the mold.

[0107] The exemplary embodiments according to FIGS. 8, 9 and 10 are onlyshown in a highly schematic manner and are therefore also describedbelow without dealing with every detail.

[0108] According to FIG. 8, the eighth exemplary embodiment also has acylinder 37 with a base 38, a small piston 28 with a restoring plate 29,and a large piston 36 which is loaded by a helical compression spring 60in the direction of the base 38 of the cylinder 37. As in the exemplaryembodiments according to FIGS. 6 and 7, in that according to FIG. 8various components also fulfill the guidance function for the largepiston 36 and the function for clamping the cylinder 37 in the bore 9.Outside the guide wall 94 for the piston 36, the cylinder 37 has anannular passage 110 in which an annular wedge 111 is locatedapproximately centrally, this annular wedge 111 bearing on the outsideagainst the guide wall 94 and running conically on the outside from itsone end face to the other end face in a conical or wedge surface 112.Located on the one side of the annular wedge 111 is an annular piston113 which, on its side remote from the annular wedge 111, defines anannular space 114 which is fluidically connected to the pressure space35 via passages 115. The annular wedge 111 has its largest outsidediameter at its axial end face facing the piston 113. A spring stack ofseveral disk springs 116 is secured in position between the end face ofthe wedge 111 having the smaller outside diameter and the one end of theannular passage 110. An outer annular wedge 117 having a conical orwedge surface 118 rests on the annular wedge 111. This annular wedge 117is held in an axially secure position in an aperture 119, leadingoutward from the annular passage 110, of the cylinder 37 and is able tobear against the wall of the bore 9. It has a slot so that it can expandradially. However, it may also be replaced by individual separate outerwedges.

[0109] In FIG. 8, the hydraulic unit 12 is shown in a state as assumedby it during the regulating movement of a movable platen of an injectionmolding machine for plastics. The restoring plate 29 of the small piston28 bears against the large piston 36 and the latter bears against thebase 38 of the cylinder 37. The pressure prevailing in the pressurespace 35 and thus also in the annular space 114 is not able to displacethe piston 113 and the wedge 111 against the disk springs 116. The wedge117 is at a small distance from the wall of the bore 9 or slides alongthe wall virtually without any applied pressure. It is not until themold is closed and the pressure in the pressure space 35 and in theannular space 114 increases above a certain value that the piston 113displaces the wedge 111 against the force of the disk springs 116, as aresult of which the wedge 117 is pressed outward against the wall of thebore 9. Since no movement can take place axially between the wedge 117and the cylinder 37, the cylinder is locked by the clamping of the wedge117 in its position. During the opening of the mold, the pressure in thepressure space 35 and in the annular space 114 decreases and the disksprings 116 are able to release the clamping between the wedges 111 and117 and thus between the wedge 117 and the machine frame. The entirehydraulic unit 12 can be moved back into its initial position.

[0110] In the ninth exemplary embodiment according to FIG. 9, as in theeighth exemplary embodiment in FIG. 8, the small piston 28, the largepiston 36, the cylinder 37 and the compression spring 60 loading thelarge piston in the direction of the base 38 of the cylinder 37 are alsoshown. The platen 125 of an injection molding machine for plastics canalso be seen, this platen 125 being fastened to the loose piston 36 andbeing guided in a movable manner on longitudinal spars 124. The spars124 also pass through the cylinder 37. Outside the spars 124, thecylinder 37, as in the exemplary embodiment according to FIG. 8, has anannular passage 110, in which an annular wedge 111 is againaccommodated, and this annular wedge 111 can be loaded in the onedirection by a piston 113 and in the opposite direction by a springstack of disk springs 116. However, this wedge 111 is now the outerwedge of two wedges and interacts with an inner wedge or several wedges117 corresponding to the number of spars. These wedges 117 are in turnaccommodated in an axially secure position in apertures 119 of thecylinder 37, which, however, now open the annular passage 110 toward thespars 124. An annular space 114 behind the annular piston 113 is againfluidically connected to the pressure space 35 by one or more connectingpassages 115. As in the exemplary embodiment according to FIG. 8, thecylinder 37 in that according to FIG. 9 is also clamped in place by theaction of the wedges 111 and 117 during a pressure increase in thepressure space 35 above a certain value. The cylinder 37 is not clampedin place toward the outside in a bore of a machine part but is nowclamped in place relative to the spars 124 guiding the platen 125.

[0111] Also in the exemplary embodiment according to FIG. 10, thecylinder 37 of the hydraulic unit 12 is clamped with the spars 124 of aninjection molding machine for plastics. The exemplary embodimentaccording to FIG. 10, in the same way as that according to FIG. 9, has asmall piston 28 and a large piston 36, to which the movable platen 125is fastened and which is loaded by the helical compression spring 60 inthe direction of the base 38 of the cylinder 37. The arrangement of thetwo wedges 111 and 117 is also the same as in the exemplary embodimentaccording to FIG. 9. However, the stack of disk springs 116 and theannular piston 113 are now transposed. The disk springs 116 act on theouter wedge 111 for clamping the cylinder 37 with the spars 124. Theannular piston 113 adjoins an annular space 126 which, in a manner notshown, can be connected via a valve to a pressure-medium source orrelieved to a pressure-medium supply reservoir.

[0112] If the annular space 126 is connected to the pressure-mediumsupply reservoir, no external force counteracts the disk springs 116.The disk springs 116 are therefore able to displace the wedge 111 to theright in the view according to FIG. 10, as a result of which the wedgeor wedges 117 are pressed against the spars 124 and the cylinder 37 isclamped with the spars 124. By the feeding of pressure medium into theannular space 126, the clamping by the wedge 117 is released against theforce of the disk springs 116.

[0113] In the exemplary embodiment according to FIG. 10, it is possible,irrespective of the build-up of pressure in the pressure space 35, toclamp the cylinder 37 in place at any desired point of the travel, e.g.at a short distance from the closing position of the platen 125. In thiscase, the clamping is ensured with a high degree of certainty, sincethis is effected via the disk springs 116 and not by a separate externaldrive. If this drive fails, the cylinder 37 is clamped immediately.

[0114] Of course, the disk springs 116 and the piston 113 may also betransposed relative to the wedges 111 and 117 in the exemplaryembodiment according to FIG. 8. It is likewise possible to reverse theinclination of the wedge surfaces 112 and 118, in which case, in orderto achieve the same functioning as in FIG. 8, the stack of disk springs116 and the annular piston 113 must of course also be transposed.

[0115] In an exemplary embodiment in which the cylinder 37 is notclamped by the pressure in the pressure space 35 but is, as it were,separately clamped, as is the case in the exemplary embodiment accordingto FIG. 10, the helical compression spring 60 need only be preloaded tosuch an extent that it can transmit the force required for acceleratingand moving the platen 125 and the cylinder 37. The pressure in thepressure space 35 builds up independently of the helical compressionspring 60.

[0116] The small piston 28 with the restoring plate 29, the large piston36, the cylinder 37, and the helical compression spring 60 of thehydraulic unit 12 can again be seen in the exemplary embodimentaccording to FIG. 11. The large piston 36, at an outer flange 45 on itsend close to the base 38 of the cylinder 37, is tightly guided in asliding manner on the envelope of this cylinder. A second guide pointhaving a small diameter is located on the flange 40 of the cylinder 37.

[0117] The cylinder 37 is not located in a bore 9 of the machine frame,which has essentially the same diameter throughout, but is now locatedin a blind hole 127 having a base 128. Formed between the latter and thebase 38 of the cylinder 37 is a second pressure space 129, the outsidediameter of which corresponds to the outside diameter of the cylinder 37and the inside diameter of which corresponds to the outside diameter ofa bush 130 in which the small piston 28 of the hydraulic unit 12 istightly guided. The bush 130 also passes through the base 128 and issealed off relative to the latter. This ensures that the pressure media,which are possibly different, from the pressure spaces 35 and 129 do notintermix.

[0118] Pressure medium from a pressure-medium supply reservoir 131 canflow to the pressure space 129. Likewise, pressure medium can bedisplaced from the pressure space 129 into the pressure-medium supplyreservoir 131. The fluidic connection between pressure space 129 andpressure-medium supply reservoir 131 is controlled with a check valve132, which stops the flow from the pressure space 129 to thepressure-medium supply reservoir 131, and a 2/2-way directional seatvalve 133 which is arranged in a bypass of the check valve 132, stopsthe flow in a rest position and can be brought into a straight-throughposition by an electromagnet. The pressure-medium supply reservoir 131may be open to the atmosphere. However, it may also be closed off fromthe atmosphere by a diaphragm 134 as indicated in figure 11a. Thediaphragm may be under a certain prestress, so that the pressure mediumis always acted upon by a pressure which is above the atmosphericpressure.

[0119] In FIG. 11, the hydraulic unit 12 is shown in a state in whichthe movable platen of an injection molding machine for plastics assumesthe end position assigned to the open mold. If the mold is now to beclosed, the piston 28, as in all the other exemplary embodiments, isalso moved to the right in the view according to FIG. 11 and in theprocess also moves the large piston 36 and the cylinder 37 in thisdirection. The pressure space 129 increases and pressure medium flowsinto it from the supply reservoir 131 via the check valve 132. If themold is closed, the pressure in the pressure space 35 increases, so thatthe cylinder 37 is acted upon by a force directed to the left. Thecylinder 37 is held in its position against this force by the pressuremedium trapped in the pressure space 129, a pressure building up in thepressure space 129 which produces a force on the base 38 of the cylinder37, this force balancing the force produced on the base 38 by thepressure in the pressure space 35 together with the force of the helicalcompression spring 60.

[0120] If the mold is to be opened, first of all the pressure in thepressure space 35 is reduced by retracting the small piston 28, as aresult of which the large piston 36 moves up to the base 38 of thecylinder 37. Then the valve 133 is put into its straight-throughposition, so that, during the subsequent retraction of the hydraulicunit 12 and the movable platen fastened to the large piston, pressuremedium can be displaced from the pressure space 129 into thepressure-medium supply reservoir 131.

[0121] In the exemplary embodiment according to FIG. 12, the movableplaten 125 is movably guided on two spars 124 and, as in the exemplaryembodiment according to FIG. 7, is connected to the large piston 36 ofthe hydraulic unit 12 via a connecting piece 104. The hydraulic unit 12is formed essentially in the same way as in the exemplary embodimentaccording to FIG. 7. One difference consists essentially only in thefact that the cylinder 37 is not formed with a double wall but ratherhas only one dimensionally stable envelope 94. In addition, thehydraulic unit 12 is not located in a bore of the machine frame butbetween the spars 124.

[0122] The spars 124 are put through a fixed supporting plate 140 at adistance from the movable platen 125 and are firmly connected to thissupporting plate 140. Also fastened to the supporting plate 140 is theelectric motor 11, which essentially corresponds to the electric motor11 from FIG. 1 or from FIG. 5 and whose parts are therefore providedwith the same designations as in FIGS. 1 and 5.

[0123] The essential difference from the motors according to FIGS. 1 and5 consists in the fact that the hollow drive shaft 19 is widened infront of the housing flange 15 to form a flange 141 which forms theinput part of a slip clutch 142. A hollow spindle 143, through which thestroke spindle 25 passes centrally, can be driven by the electric motor11 via this slip clutch 142, and this hollow spindle 143 is providedwith an external thread 144 having the same pitch as the external thread27 of the stroke spindle 25 and has a flange 145 axially opposite theflange 141. The hollow spindle 143 is axially supported on the hollowshaft 19 of the electric motor via a rolling-contact bearing 146. Thehollow shaft 19 in turn is supported on the supporting plate 140 via arolling-contact bearing 147. The rolling-contact bearing 146 and theslip clutch 142 are matched to one another in such a way that thefriction linings of the slip clutch can only be pressed against oneanother up to a certain force. Forces exceeding this force aretransmitted directly to the hollow shaft 19 via the rolling-contactbearing 146. The external thread 144 of the hollow spindle 143 is inengagement with the internal thread 148 of a spindle nut 149 which isguided on the spars 124 and acts as an axial stop for the cylinder 37.Secured in position between the latter and the spindle nut 149 is ahelical compression spring 150 which attempts to push the two partsapart axially, the distance between the two parts possibly being a fewtenths of a mm. The position of the restoring plate 29 on the smallpiston 28 is of course designed for such a distance. The threads 144 and148 are Trapezoidal threads which intermesh in a self-locking manner.

[0124] To close the mold, the electric motor 11 drives the strokespindle 25 via the hollow shaft 19 and at the same time the hollowspindle 143 via the slip clutch 142. Since the intermeshing threadsbetween hollow shaft 19 and stroke spindle 25 have the same pitch as theintermeshing threads 144 and 148 of hollow spindle 143 and spindle nut149, the spindle nut 149 moves at the same speed as the stroke spindle25. It thus runs behind the cylinder 37 of the power transmission means12 at the distance ensured by the spring 150.

[0125] As soon as the mold is closed, the pressure in the pressure space35 increases, so that the cylinder 37 gives way to the rear until theclearance between it and the spindle nut 149 has been used up. Furtherrotation of the hollow shaft 19 leads to an increase in the moment inthe Trapezoidal threads 144 and 148. The slip clutch 142 slips, so thatsubsequently only the small piston 28 of the hydraulic unit 12 continuesto be moved and, since the cylinder 37 is axially supported via thespindle nut 149, the closing force is produced by build-up of pressurein the pressure space 35 via the large piston 36 of the hydraulic unit12.

[0126] During opening of the mold, the hollow shaft 19 rotates in theopposite direction, so that the small piston 28 is moved back and thepressure in the pressure space 35 is reduced. The compression spring 150pushes the cylinder 37 up to the piston 36 and the latter up to therestoring disk 29 and resets the distance between the cylinder 37 andthe spindle nut 149. The moment in the screw drive 144, 149 drops, theslip clutch 142 engages and the spindle nut 149 is moved back via thehollow spindle 143.

[0127] If it is to be possible to be able to stop the spindle nut 149irrespective of the increase in the friction moment between it and thehollow spindle 143, a brake 150 may be provided for the hollow spindle143, as indicated in FIG. 12. There, the flange 145 of the hollowspindle 143 is enlarged outward to form a type of brake disk, againstwhich brake shoes 151 can be pressed. The cylinder 37 of the hydraulicunit 12 can then be supported in a position which does not correspond tothe closing position of the platen 125.

[0128] The exemplary embodiment according to FIG. 13, with regard to thefixed supporting plate 140, the spars 124, the movable platen 125, isidentical to the exemplary embodiment according to FIG. 12. The electricmotor 11 is largely the same as the electric motor 11 from FIG. 12 butnow again has a simple hollow drive shaft 19. Its housing 13, unlike thepreviously shown electric motors 11 from FIGS. 1, 5 and 12, is providedwith an extension 155 which points toward the hydraulic unit 12 and hasan external thread 156. The construction of the hydraulic unit 12according to FIG. 13 is in principle identical to the construction ofthe hydraulic unit according to FIG. 12. An outer flange 157 of thecylinder 37 is merely set back slightly relative to an end face of thecylinder.

[0129] A rolling-contact thrust bearing 159 is arranged between theflange 157 and a plate 158 which is located in front of this flangetoward the electric motor 11 and is rotatable relative to the cylinder37, via which rolling-contact thrust bearing 159 the plate and thecylinder can be supported axially against one another. The plate 158 iscoupled in the direction of rotation to a nut 160 which, with aninternal thread 161, engages in the external thread 156 of the housingextension 155. The two threads 156 and 161 are again formed so as to beself-locking. Secured axially in position between the nut 160 and theplate 158 is a compression spring which has the same function as thecompression spring 150 from FIG. 12 and is therefore likewise providedwith the designation 150. This compression spring attempts to hold theplate 158 at a small axial distance of a few tenths of a mm from the nut160. For the rotary driving, the nut 160, with individual claws, engagesin the plate 158, the axial distance also existing between the claws andthe plate 158. The nut 160 is provided on the outside with a toothsystem, with which it meshes with a gear 162 which can be driven by asecond, smaller electric motor 163. The electric motor 163 is arrangedin a fixed position. The gear 162 has the appropriate axial length, sothat it remains in engagement with the nut 160 within the entire rangeof movement of the latter.

[0130] During the closing of the mold, the electric motor 11 and theelectric motor 163 are driven at such rotational speeds that the spindle25 and the nut 160 move forward with the same axial speed. The smalldistance between the nut 160 and the plate 158 ensures that thehydraulic unit 12 is not loaded via the nut 160 and possible jamming ofthe drives does not occur. Since the rotational speeds of the electricmotors 11 and 163 are selectable, the threads 156 and 161 need not havethe same pitch as the external thread on the stroke spindle 25 and theinternal thread on the hollow shaft 19 of the electric motor 11.Otherwise, the sequence of movement in the exemplary embodimentaccording to FIG. 13 is the same as in that according to FIG. 12, sothat reference shall be made here only to the corresponding parts of thedescription.

[0131] There are also two electric motors in the exemplary embodimentaccording to FIG. 14 in order to drive, firstly, a stroke spindle 25which has a section constituting the small piston 28 of the hydraulicunit 12 and an axial stop for the cylinder 37 of the hydraulic unit 12.In a different manner from that shown previously, the electric motor 170for the drive of the recirculating ball spindle 25 is now arranged in afixed position eccentrically to the latter and drives a spindle nut 172via a pinion 171, this spindle nut 172 having an internal thread whichis in engagement with the thread of the screw spindle 25 via balls 28.To this extent, the spindle nut 172 fulfills the function of the hollowshaft 19 of exemplary embodiments already described and, like thelatter, is also axially supported via a rolling-contact bearing 147.

[0132] A hollow spindle 174 is rotatably mounted on the spindle nut 172via radial bearings 173. This hollow-spindle is supported axially on thespindle nut 172 via a rolling-contact thrust bearing 175 and maintainsits axial position during operation. It is provided in sections on theoutside with a tooth system 176, with which it meshes with a pinion 162which can be driven by the electric motor 163. In addition, the hollowspindle 174 is provided on the outside in sections with a trapezoidalthread 144, with which it engages in a trapezoidal thread 148 on theinside on a hollow body 177 formed in one piece with the cylinder 37 ofthe 59 hydraulic unit. The engagement of the threads 144 and 148 isagain self-locking.

[0133] With regard to the large piston 36, the helical compressionspring 60 and the engagement of a restoring plate 29 of the small piston28 on individual inwardly projecting claws 178 of the large piston 36,the exemplary embodiment according to FIG. 14 is identical to thataccording to FIG. 11.

[0134] In the exemplary embodiment according to FIG. 14, in order toclose the mold, the two electric motors 163 and 170 are operated at suchrotational speeds that the rate of motion imposed on the cylinder 37 viathe stroke spindle 25 is identical to that which results from therotation of the hollow spindle 174 relative to the hollow body 177,which is guided longitudinally in a rotationally locked manner with thecylinder 37. In this case, there is certain play in the threads 144 and148, which has the function of the axial distance between the spindlenut 149 and the cylinder 37 in the exemplary embodiment according toFIG. 12 and between the nut 160 and the plate 158 in the exemplaryembodiment according to FIG. 13. The hollow spindle 147 is thus onlyfreely rotated by the electric motor 163.

[0135] To close the mold, the electric motor 170 drives the spindle nut172, so that the spindle 25 and with it the large piston 36 and, carriedalong via the helical compression spring 60, the cylinder 37 travel inthe closing direction. The electric motor 163 is driven in such a waythat the movement of the cylinder 37 is not impaired by the rotation ofthe hollow spindle 174. If the mold is closed, the electric motor 163 isstopped, and the cylinder 37, via the thread turns still in engagement,is supported on the hollow spindle 174 and via the latter is supportedon the frame of the machine via the rolling-contact bearing 175, thespindle nut 172 and the rolling-contact bearing 147 when the highlocking pressure is built up by further plunging of the small piston 28into the pressure space 35.

[0136] During the opening of the mold, first of all the pressure in thepressure space 35 is reduced by retraction of the small piston 28, sothat the piston 28 again moves up to the cylinder 37 and carries thelatter along to the rear. The electric motor 163 is driven in theopposite direction compared with the closing of the mold and freelyrotates the hollow spindle 174 with it.

[0137] The exemplary embodiment according to FIG. 15, in theconstruction of the cylinder 37 of the hydraulic unit 12, is similar tothe exemplary embodiment according to FIG. 7. The cylinder 37 has a base38, a flange 40 and an inner tube 94, which runs between these two partsand which has a large wall thickness and is accordingly dimensionallystable, and a thin-walled outer tube 92 surrounding the tube 94. Thebase 38 and flange 40 overlap the end faces of both the tube 94, towhich they are firmly screwed with machine screws, and the tube 42,which is held axially free of clearance between base and flange. Axiallywithin two radial seals which are arranged close to the base and flangebetween the two tubes 92 and 94, there is a small distance between thetwo tubes which has produced an annular admission space 183.

[0138] According to FIG. 15, the large piston 36 is formed as a steppedpiston and is axially guided in the tube 94 approximately in the centerof its longitudinal extent at the section 181 having the large diameter.With the section 182 of smaller diameter, the piston 36 projects fromthe cylinder 37 through the flange 40. The piston 36 may also be axiallyguided at the section 182, for example on the flange 40. A helicalcompression spring 60 is secured in position at the step between the twosections 181 and 182 of the piston 36, on the one hand, and at an innercollar of the tube 94 of the cylinder 37, on the other hand, thishelical compression spring 60 loading the piston 36 and the cylinder 37for retracting the piston 36 into the cylinder 37. The space in whichthe spring 60 is located is open to the atmosphere. Close to the step,in addition to the guidance point, a sealing point is also locatedbetween the section 181 of the piston 36 and the tube 94 of the cylinder37. In front of the guidance and sealing point, the section 181 of thepiston 36 is turned down slightly on the outside up to the end face 184facing the base 38 of the cylinder 37. The annular space which isproduced as a result is part of the pressure space 35. Leading throughthe tube 94 are radial holes 98, via which the admission space 183 isfluidically connected to said annular space and thus to the pressurespace 35.

[0139] The small piston 28 of the power transmission means 12 enters thepressure space 35 through a guide and sealing bush 185 inserted into thebase 38 of the cylinder 37 and projects into the piston 36. In thelatter, the small piston 28 first of all crosses a cavity (clutch space)186 of circular-cylindrical cross section before it plunges into a blindhole 56 starting from the cavity. The blind hole 56, via passages 187 inthe piston 36, which open freely into said blind hole 56 irrespective ofthe relative position of the two pistons, is connected to the outerannular space at the section 181 and thus to part of the pressure space35. Inside the clutch space 186, the cross-sectional area of which issubstantially larger than the cross-sectional area of the piston 28 andwhich is sealed off both toward the space in front of the end face 184of the piston 36 and toward the blind hole 56 in each case by a sealbetween the pistons 28 and 36, the piston 28 carries a separating disk188 which divides the clutch space 186 into two sectional spaces sealedoff from one another. Two check valves 189 and 190 used as clampingvalves are inserted into the separating disk in an antiparallelarrangement, the closing springs of these check valves 189 and 190 beingpreloaded to a pressure of, for example, up to 20 bar. The preloading ofthe two closing springs is different. The small piston 28 has the samediameter on both sides of the separating disk 188, so that, with theseparating disk 188 included, it forms with the large piston a type ofsynchronous cylinder. The parts just described form a hydraulic slipclutch 180 which firmly couples the two pistons to one another up to acertain force to be transmitted, which is different in the opposeddirections.

[0140] Also in the exemplary embodiment according to FIG. 15, the smallpiston 28 is a section of a stroke spindle 25 which is locked againstrotation. The stroke spindle interacts with a spindle nut 192 mounted onthe machine frame 10 independently of the electric motor 11. Theelectric motor 11 is a conventional variable-speed motor, is fastened tothe machine frame outside the axis of the stroke spindle 25 and drivesthe spindle nut 192 via a belt 193.

[0141] In FIG. 15, the hydraulic unit is shown in a state in which themold of an injection molding machine for plastics is completely open.The large piston 36, with its end face 184, is located at the base 38 ofthe cylinder 37 preferably via short spacers. The small piston 28assumes a position in which the separating disk 188 is located at theend of the clutch space 186. If the mold is now to be closed, the smallpiston 28 and with it the separating disk 188 are moved to the right inthe view according to FIG. 15 by appropriate activation of the electricmotor 11. The movement of the separating disk, via the pressure fluid inthe clutch space 186, this pressure fluid being prestressed to a certainpressure, is transmitted directly to the large piston 36 and thus to themovable platen. The large piston 36 also carries along the cylinder 37via the helical compression spring 60. The pressure in the pressurespace 35 does not change.

[0142] Once the mold has finally been closed, a high resistance opposesthe further movement of the large piston 36. The piston 28, on the otherhand, continues to move and plunges deeper into the blind hole 56, fromwhich pressure fluid is displaced via the passages 187. As a result, thepressure in the pressure space 35 increases. First of all, the helicalcompression spring 60, preloaded to an appropriately high degree, stillprevents the cylinder 37 from giving way to the left. Finally, byfurther pressure increase in the pressure space 35, the outer tube 92 iswidened, so that it abuts against the wall of the bore 9 on the inside.The cylinder 37 is then held by clamping in the bore 9, so that, byfurther movement of the small piston 28, the pressure in the pressurespace 35 can be increased further in order to exert a high locking forcefor the mold. During the movement of the piston 28 relative to thepiston 36, pressure fluid, via the one check valve 189, flows over froma (first) sectional space into the other (second) sectional space of theclutch space 186.

[0143] To open the mold, the electric motor 11 is driven in the oppositerotary direction, so that the piston 28, as viewed according to FIG. 15,moves to the left. The check valve 190 is only slightly preloaded andopens, so that pressure fluid can flow back inside the clutch space 186from the second sectional space into the first sectional space. Thepressure in the pressure space 35 is reduced. Finally, the piston 28carries along the piston 36 and the latter carries along the cylinder 37in the opening direction of the mold.

[0144] Also in the exemplary embodiment according to FIG. 16, thecylinder 37 of the power transmission means 12 has a base 38, a flange40 and an inner dimensionally stable tube 94 running between these twoparts and a thin-walled outer tube 92 surrounding the tube 94. Unlike inthe exemplary embodiment according to FIG. 15, however, the tube 92 doesnot itself bear directly against the wall of the machine frame 10.Rather, the tube 92 is surrounded on the outside by a plurality ofindividual brake rods 196 which, when resting on the relieved tube 92,complement one another to form a closed ring and which are overlappedradially by the base 38 and the flange 40 and are held axially betweenbase and flange with slight play which permits their free mobility inthe radial direction. Each brake rod 196 is provided with a brake lining197 on the outside. In the relieved state of the tube 92, the brake rodsare at a distance from the wall of the machine frame 10. Again locatedbetween the tubes 92 and 94 is the annular admission space 183, which isfluidically connected to the pressure space 35 via radial holes 98running through the tube 94.

[0145] Compared with the representation according to FIG. 15, the largepiston 36 is depicted in slightly more detail from the design point ofview in FIG. 16. A two-piece construction of the piston 36 can be seenin FIG. 16, the one part 182 having essentially a small diameter andemerging outward through the flange 40, and the other part 181 with thelarger diameter serving to guide the piston and seal off the pressurespace 35. A helical compression spring 60 is again secured in positionbetween the piston 36 and the cylinder 37.

[0146] Like the piston 36 from FIG. 15, the piston 36 of the exemplaryembodiment according to FIG. 16 also has in the interior a cavity(clutch space) 186 which accommodates a coupling device 195 for couplingthe two pistons 36 and 28. This coupling device is anelectromagnetically actuated clutch, the electric coil 198 of which isaccommodated by an annular groove 199 which is open toward the space 186and is sunk into that wall of the piston 36 which closes off the clutchspace 186 toward the base 38 of the cylinder 37. The clutch space 186 isconnected to the atmosphere via holes 200 and the space accommodatingthe spring 60.

[0147] The small piston 28, with a certain diameter, enters the pressurespace 35 in a sealed-off manner through the base 38 of the cylinder 37.Its cross section is reduced therein in a step 201, following which is apiston extension 202 of smaller diameter. After crossing a blind hole 56of the piston 36, this blind hole 36 being open toward the base 38 ofthe cylinder 37 and its diameter being so large that the piston 28 canplunge into it with its larger diameter, the piston extension 202 entersthe clutch space 186 in a sealed-off manner. Inside this space, anarmature plate 203 of the clutch 195 is fastened to the pistonextension. The yoke of the electromagnetic clutch 195 is formed by theone part of the piston 36.

[0148] In FIG. 16, the hydraulic unit is shown in a state in which themold of an injection molding machine for plastics is completely open.The large piston 36, with its end face 184, is located at the base 38 ofthe cylinder 37 via short spacers. The small piston 28 assumes aposition in which the armature plate 203 is located at the yoke. If themold is now to be closed, the coil 198 is energized, that is to say theclutch 195 comes into effect and the small piston 28 is moved to theright in the view according to FIG. 16 by appropriate activation of theelectric motor 11. Via the armature plate 203, the large piston 36 iscarried along synchronously and thus the movable platen is moved. Thelarge piston 36 also carries along the cylinder 37 via the helicalcompression spring 60. The pressure in the pressure space 35 does notchange.

[0149] Once the mold has finally been closed, a high resistance opposesthe further movement of the large piston 36. The coil 198 isde-energized. The piston 28 continues to move and plunges deeper intothe blind hole 56 and displaces pressure fluid with its annular surface201. As a result, the pressure in the pressure space 35 increases. Firstof all, the helical compression spring 60, preloaded to an appropriatelyhigh degree, still prevents the cylinder 37 from giving way to the left.Finally, by further pressure increase in the pressure space 35, theouter tube 92 is widened, so that the brake rods 196 abut on the insideagainst the wall of the bore 9. The cylinder 37 is then held by clampingin the bore 9, and the pressure in the pressure space 35 can beincreased further by further movement of the small piston 28, so thatthe preloading force of the spring 60 is overcome and the high lockingforce for the mold is built up.

[0150] To open the mold, the electric motor 11 is driven in the oppositerotary direction, so that the piston 28, as viewed according to FIG. 16,moves to the left. In the process, the piston 36 is also carried alongwithout engaged clutch 195.

[0151] The exemplary embodiment according to FIG. 19 is completelyidentical to the exemplary embodiment according to FIG. 16 insofar asthis has just been described. To this extent, therefore, the samedesignations have been entered without the description being repeatedhere.

[0152] Unlike the exemplary embodiment according to FIG. 16, thecylinder 37 of the hydraulic unit 12 in that according to FIG. 19 canalso be locked without a resistance which opposes the movement of thelarge piston 36. To this end, the machine frame has individual radialopenings 210 which are distributed over the periphery of the bore 9 andopen into the latter and into which brake shoes 211 which can be loadedhydraulically toward the inside are inserted. On the outside, eachopening 210 is closed by a cap 212 having a central connection hole 213.Via the latter, external pressure fluid, that is pressure fluid which isnot exchanged with the pressure space 35, can pass into the admissionspaces 183 between the brake shoes and the caps and flow off from there.The hydraulic circuit for the pressure-medium supply of the brake shoes211 is a closed circuit and comprises a hydraulic pump 214 of constantstroke volume, which can be driven by a small electric motor 209, alow-pressure hydraulic accumulator 215 in a low-pressure branch and ahigh-pressure hydraulic accumulator 216 in a high-pressure branch of thecircuit. The high-pressure branch, via a 2/2-way directional seat valve217, and the low-pressure branch, via a 2/2-way directional seat valve218, can be connected to the admission spaces 183 or can be shut offfrom the latter. The two valves 217 and 218 are each actuated by anelectromagnet. Arranged between the hydraulic accumulator 216 and thehydraulic pump 214 is a check valve 219 shutting off toward the latter,so that the hydraulic accumulator 216 does not discharge via thehydraulic pump when the latter is stopped. The hydraulic components 214,215, 216, 217, 218 and 219 are located in a fixed position on themachine frame 10.

[0153] The cylinder 37 has a base 38 enlarged like a pot and having anenvelope 220 which is so long that the brake shoes 211 can be pressedagainst it within the range of movement provided in every position ofthe cylinder.

[0154] The exemplary embodiment according to FIG. 19 functions inexactly the same way as that according to FIG. 16. However, the cylinder37 can be locked at any desired point even without a motion resistancefor the large piston 36. Because no pressure is required in the pressurespace 35 for locking the cylinder 37, the spring can be preloaded solelyfrom the point of view that it can transmit the force required forcarrying along the cylinder 37 by the piston 36 as far as possiblewithout said spring having to be compressed further. The cylinder 37then follows the piston 36 directly. It is then also conceivable toinitially lock the cylinder with the brake shoes 211 and a relativelylow external pressure and primarily by admission of pressure to the tube92 after a pressure increase in the pressure space 35.

[0155] In addition, when the brake shoes 211 are to be inoperative, thevalve 218 is operated, as shown in FIG. 19. The pressure in thelow-pressure accumulator is slightly above atmospheric pressure, so thatthe brake shoes bear against the envelope 220 with a fairly low force.In order to press the brake shoes 211 against the cylinder 37, the valve218 is put into the shut-off position and the valve 217 is opened. Thecompression quantity required for the pressure increase can now flowfrom the hydraulic accumulator 216 toward the admission spaces 183behind the brake shoes 211. The brake acts very quickly.

[0156] The drive device according to FIG. 19 is especially suitable for“injection-compression molding”. In this case, a movable platen is movedup close to a fixed platen by the piston 28 being moved when the clutch195 is effective. The cylinder 37 is then locked by admission ofpressure to the brake shoes 211. A molding compound is then injectedbetween the two mold halves, the piston 36 being supported by bearingagainst the base 38 of the cylinder 37 and by the latter being lockeddirectly on the machine frame 10. To compress the injected moldingcompound, the small piston 28, with clutch 195 released, is movedfurther and as a result the large piston 36 is moved together with themovable platen until coming to bear against the fixed platen, in thecourse of which the pressure in the pressure space 35 can be built up toa desired value.

[0157] From the design point of view, the exemplary embodiment accordingto FIG. 20 is largely identical to the exemplary embodiment according toFIG. 16 insofar as this has been described above. To this extent,therefore, the same reference numbers are entered without thedescription being repeated here.

[0158] The difference consists in the fact that, in the exemplaryembodiment according to FIG. 20, there are no radial holes 98 passingthrough the tube 94, and external pressure medium can be fed to theannular admission space 183 between the two tubes 92 and 94 via aconnection passage 221 leading outward through the tube 94 and the base38. The hydraulic circuit for the pressure loading and relief of theadmission space 183 is constructed in exactly the same way as in theexemplary embodiment according to FIG. 19 and comprises the hydraulicpump 214, which can be driven by the electric motor 209, the hydraulicaccumulators 215 and 216 and also the valves 217, 218 and 219. Thesecomponents are not fastened to the machine frame 10 but are now fastenedto the cylinder 37, so that fixed bores or fixed tubing can be providedfor the fluid paths of the circuit.

[0159] The functioning of the exemplary embodiment according to FIG. 20corresponds to that of the exemplary embodiment according to FIG. 19, itbeing possible for a spring 60 subjected to relatively low preloading tobe used again, since the pressure in the admission space 183 is built upindependently of the spring force.

[0160] The construction of the exemplary embodiment according to FIG.21, with regard to the clamping of the cylinder 37, is identical to theexemplary embodiment according to FIG. 16, so that the description inthis respect can be dispensed with here. However, the correspondingdesignations are entered in FIG. 21.

[0161] Also in the exemplary embodiment according to FIG. 21, as in thataccording to FIG. 16, a small piston, which is designated by 228 onaccount of the completely different configuration from the exemplaryembodiment according to FIG. 16, and the large piston 36 may be directlycoupled to one another via an electromagnetically actuable clutch 195which is located in a cavity (clutch space) 186 of the large piston. Theelectric coil 198 is again accommodated by an annular groove which isopen toward the space 186 and is sunk in that end wall of the piston 36which closes off the clutch space 186 toward the base 38 of the cylinder37. The large piston 36, with a piston rod 42 which is smaller than theeffective piston diameter and whose length is matched to the stroke,required for closing the mold, of the hydraulic unit 12 and which isfastened to the movable platen (not shown), emerges from the cylinder 37through the flange 40 of the latter. The piston rod is hollow throughoutfrom its outer end right into the clutch space 186, the cavity beingdesignated by 231 and being essentially circular in cross section. Anarrow groove 232 runs axially along merely in the wall of the cavity.The clutch space 186 is connected to atmosphere via the cavity 231.

[0162] The small piston 228 is composed essentially of three hollowdisk- or bush-shaped parts and is very short overall. A first bush 233is guided with a certain diameter in the base 38 of the cylinder 37 insuch a way as to be sealed off to the outside. The cross section of thebush 233 decreases in a step or annular surface 201 which, in the stateshown in FIG. 21 and corresponding to an open injection mold, is locatedinside the base 38 and, depending on the travel of the small pistonrelative to the large piston during the build-up of the locking force,remains in the base or emerges more or less from the base. Therespectively free annular space in front of the annular surface 201 ispart of the pressure space 35 defined by the two pistons and thecylinder. With the smaller cross section, the bush 233 enters the clutchspace 186 in a sealed-off manner through the above-mentioned end wall ofthe large piston 36 and has an adjoining external thread on an extensionwhich is stepped once again.

[0163] A second bush 234 of the piston 228 is formed as a spindle nutand is guided in an axially displaceable manner in the cavity 231 of thelarge piston 36 via a plain bearing 235. In the state of the hydraulicunit 12 according to FIG. 21, the spindle nut 234 is located at that endof the cavity 231 which opens into the clutch space 186. Toward the part233, the spindle nut 234 has an extension which is provided with aninternal thread and with which it is screwed to the bush 233. A disk203, as a third part of the piston 228, is clamped in place axiallybetween the extension of the spindle nut 234 and the bush 233, this disk203 extending radially beyond the coil 198 and forming the armature ofthe clutch 195. With a radially projecting nose 236, the spindle nut 234engages in the groove 232 of the piston 36, so that the small piston 228cannot be rotated relative to the large piston 36. Since, on the otherhand, the large piston is locked against rotation by the connection tothe movable platen, the small piston 228 cannot rotate either. Theclutch space 186 may be connected to atmosphere by, for example, a holein the nose 236.

[0164] The hydraulic unit 12 is located in a tube 240 which is closed onboth sides by a respective flange 241. Only the flange 241 toward whichthe base 38 of the cylinder 37 faces is shown in FIG. 21. The piston rod42 can emerge from the tube 240 through the other flange. Arolling-contact bearing 242 is inserted into a central passage of theflange 241.

[0165] In a completely different manner from the exemplary embodimentsdescribed hitherto, the stroke spindle 25 is not arranged axially nextto the hydraulic unit 12 and in front of the small piston, but nowextends from an outer circular-cylindrical drive stub 243, which passeswith an interference fit through the rolling-contact bearing 242 andprojects outward beyond the flange 241, through the hollow small piston228 and the hollow large piston 36 up to the other end of the tube 240.The stroke spindle 25, starting from a point close to the flange 241 andextending up to the other end, is provided with a recirculating ballscrew, in which balls run along, which on the other hand also engage inthe thread of the spindle nut 234 formed as a recirculating ball sleeve.The stroke spindle 25 cannot move axially but can only be driven in arotational manner. To this end, a toothed disk 244 is fastened to thedrive stub 243, and this toothed disk 244 is coupled via a toothed belt246 to a second toothed disk 247 fastened to the drive shaft 245 of anelectric motor 11. The electric motor 11 is located outside the tube 240on the same side of the toothed disks 244 and 247 as the tube and isconnected to the latter by a fastening flange 248, put onto the flange241 and screwed together with the flange 241 to the tube 240, to form aconstruction unit.

[0166] It may also be mentioned that, in the exemplary embodimentaccording to FIG. 21, the helical compression spring 60 from thepreceding exemplary embodiments is replaced by a disk spring stack 60.

[0167] In addition, it is also indicated in FIG. 21 that the powersupply to the coil 198 is effected via a bore in the base of the piston36, a tube 249 bridging the clutch space 186 outside the armature 203, afurther bore in the piston 36, an annular space between the piston 36and the cylinder 37, a bore in the cylinder 37 and an axial bore throughthe flange 40.

[0168] In FIG. 21, the hydraulic unit is shown in a state in which themold of an injection molding machine for plastics is completely open.The large piston 36, with its end face 184, is located at the base 38 ofthe cylinder 37 via short spacers. The small piston 228 assumes aposition in which the armature plate 203 is located at the yoke. If themold is now to be closed, the coil 198 is energized, that is to say theclutch 195 is engaged. The electric motor 11 rotates the stroke spindle25 in such a direction that the recirculating ball sleeve 234 and thusthe entire small piston 228 is moved to the right in the view accordingto FIG. 21. Via the armature plate 203, the large piston 36 is carriedalong synchronously and thus the movable platen is moved. The largepiston 36 also carries along the cylinder 37 via the disk spring stack60. The pressure in the pressure space 35 does not change.

[0169] Once the mold has finally been closed, a high resistance opposesthe further movement of the large piston 36. The coil 198 isde-energized. The piston 228 continues to move and displaces pressurefluid with its annular surface 201. As a result, the pressure in thepressure space 35 increases. First of all, the disk spring stack 60,preloaded to an appropriately high degree, still prevents the cylinder37 from giving way to the left. Finally, by further pressure increase inthe pressure space 35, the outer tube 92 is widened, so that the brakerods 196 abut on the inside against the tube 240. The cylinder 37 isthen held by clamping in the tube 240, and the pressure in the pressurespace 35 can be increased further by further movement of the smallpiston 228, so that the preloading force of the disk spring stack 60 isovercome and the high locking force for the mold is built up.

[0170] To open the mold, the electric motor 11 is driven in the oppositerotary direction, so that the piston 228, as viewed according to FIG.21, moves to the left. In the process, the piston 36 is also carriedalong without engaged clutch 195.

[0171] The construction of the exemplary embodiment according to FIG.22, with regard to the clamping of the cylinder 37 and the arrangementof the screw spindle 25, the hydraulic unit 12 and the electric motor11, is identical to the construction of the exemplary embodimentaccording to FIG. 21, so that a description in this respect can bedispensed with here. However, the corresponding designations are enteredin FIG. 22. The exemplary embodiment according to FIG. 22 is describedbelow essentially only with regard to the differences from the exemplaryembodiment according to FIG. 21.

[0172] There is a spindle nut in the form of a recirculating ball sleeve253, which is located in a central passage of the cylinder flange 38 andis provided with an outer shoulder 254 in front of this flange 38. Onthe flange side, a hardened supporting disk 255 rests on the outershoulder 254, and supported on said supporting disk 255 at equal angulardistances apart are a plurality of little pistons 256, which are guidedaxially in holes, open toward the pressure space 35, of the flange 38,are pressed against the disk 255 by springs (not shown in any moredetail in FIG. 22) and form in their entirety the small piston of thehydraulic unit 12. The pressure space 35, in the exemplary embodimentaccording to FIG. 22, comprises an annular sectional space which isdefined radially on the outside by the cylinder tube 94, radially on theinside by a collar 257 integrally formed on the flange 38, and axiallyon the one side by the flange 38 and on the other side by an annularsection 258, plunging in a sealed-off manner between the cylinder wall94 and the collar 257, of the large piston 36.

[0173] Screwed into the cylinder flange 38 from outside is a smallpiston accumulator 260 which has a piston 261 which separates a pressurefluid space 262, fluidically connected to the pressure space 35 throughthe flange 38, from an air space 263 connected to atmosphere.Accommodated in the air space 263 is a helical compression spring 264which loads the piston 261 in the direction for reducing the pressurefluid space 262. The travel of the piston 261 in the direction forincreasing the pressure fluid space 262 and for greater loading of thespring 264 is limited by a stop in such a way that a pressure within therange of 5 to 10 bar in the pressure space 35 corresponds to the springforce when the piston 261 bears against the stop. This pressure is lowerthan the pressure equivalent to the force of the disk spring stack 60.With the piston accumulator 260, volumetric changes of the pressurefluid located in the pressure space 35 which accompany temperaturechanges can be compensated for without a substantial pressure change. Onthe other hand, if a pressure is to be built up in the pressure space 35by retraction of the little pistons 256, pressure fluid can no longer bedisplaced into the piston accumulator 260 as soon as the piston 261 hasreached the stop. The idle stroke of the little pistons 256 which is dueto the piston accumulator 260 is therefore only small.

[0174] Whereas the electromagnetic clutch 195 in the exemplaryembodiment according to FIG. 21 is arranged between the spindle nut andthe small piston on the one hand and the large piston on the other hand,such a clutch in the exemplary embodiment according to FIG. 22 islocated between the spindle nut 253 and the small piston 256 on the onehand and the cylinder 37 of the hydraulic unit 12. To this end, a yokedisk 267 located on the outside of the cylinder flange 38 and having acoil 198 is firmly held on the cylinder 37 at a distance from the flangevia rods 268. An armature plate 203, which is fastened to the spindlenut 253, is located between the yoke disk 267 and the flange 38 and isfirmly held on the yoke disk when the coil 198 is energized, so that thespindle nut 253 is then coupled to the cylinder 37 of the hydraulic unit12.

[0175] In the exemplary embodiment according to FIG. 22, the second endof the screw spindle 25 is provided with a bearing journal 269, ontowhich the inner ring of a rolling-contact bearing 270 is pressed. Theouter ring of the rolling-contact bearing is guided longitudinally inthe cavity 231 of the large piston 36 and is locked against rotation. Bythe bearing 270, wobbling movements of the screw spindle 25 and thusaccompanying alternating loading of the screw drive are avoided.

[0176] In FIG. 22, the hydraulic unit 12 is shown in a state in whichthe mold of an injection molding machine for plastics is completelyopen. The large piston 36 is located at the flange 38 of the cylinder37. The little pistons 256 assume a position in which the armature plate203 is located at the yoke disk 267. If the mold is now to be closed,the coil 198 is energized, that is to say the clutch 195 is engaged. Theelectric motor 11 rotates the stroke spindle 25 in such a direction thatthe recirculating ball sleeve 253 and thus the little pistons 256 aremoved to the right in the view according to FIG. 22. Via the armatureplate 203, the cylinder 37 and, via the latter, the large piston 36 arecarried along synchronously and thus the movable platen is moved. In themeantime, the pressure in the pressure space 35 does not change.

[0177] If the mold has finally been closed, a high resistance opposesthe further movement of the large piston 36. The coil 198 isde-energized. The spindle nut 253 and the little pistons 256 continue tomove and displace pressure fluid. As a result, the pressure in thepressure space 35 increases. The piston 261 of the piston accumulator260 reaches its stop. First of all, the disk spring stack 60, preloadedto an appropriately high degree, still prevents the cylinder 37 fromgiving way to the left. Finally, by further pressure increase in thepressure space 35, the outer tube 92 is widened, so that the brake rods196 abut on the inside against the tube 240. The cylinder 37 is thenheld by clamping in the tube 240, and the pressure in the pressure space35 can be increased further by further movement of the little pistons256, so that the preloading force of the disk spring stack 60 isovercome and the high locking force for the mold is built up.

[0178] To open the mold, the electric motor 11 is driven in the oppositerotary direction, so that the spindle nut 253, as viewed according toFIG. 22, moves to the left. In the process, the cylinder 37 and, by thecylinder 37 via the disk spring stack 60, the large piston 36 are alsocarried along without engaged clutch 195. The little pistons 256 followthe supporting plate 253 on account of the springs which load them.

[0179] If the one end of the screw spindle 25, as can be seen from FIG.22, is mounted directly in the large piston 36 via a rolling-contactbearing, the large piston 36 and the screw spindle must be in veryprecise alignment with one another, which requires high-precision andthus expensive production. On the other hand, a type of bearingarrangement according to FIG. 23 permits alignment errors between piston36 and screw spindle 25 but at the same time prevents wobbling movementsof the screw spindle. To this end, a radial movement of therolling-contact bearing 270 and of the spindle end is permitted if theacting transverse force exceeds a certain magnitude.

[0180] According to FIG. 23, the outer ring 271 of the rolling-contactbearing 270 is pressed into a bush 272, the outside diameter of which issmaller than the diameter of the cavity 231 and which, with an innercollar 273, is located axially between two friction disks 274 and 275.The latter are guided one inside the other and are loaded toward oneanother by a spring 276 secured in position between them, so that theinner collar 273 of the bush 272 is clamped in place with a certainforce between the two friction disks. The friction disk 274 is guidedlongitudinally in the piston 36 with tight radial clearance and islocked against rotation in the process.

[0181] Small forces which could be the cause of a wobbling movementwhile the screw spindle is being rotated cannot overcome the frictionforces acting between the bush 272 and the friction disks 274 and 275,so that, to this extent, the end of the screw spindle 25 is kept steadyand the type of bearing arrangement is that of a fixed bearing. However,an alignment error between the screw spindle 25 and the large piston 36,which alignment error will also change with a change in the relativeposition of the large piston relative to the screw spindle during aworking cycle, causes transverse forces between the friction partners272, 274 and 275 which exceed the friction forces and lead to a changein position between the bush 272 on the one hand and the friction disks274 and 275 on the other hand, so that the bending stress, caused by thealignment error, of the screw spindle 25 and the stress of theirbearings remains limited.

[0182] The exemplary embodiment according to FIG. 24, with regard to itsmechanical construction, corresponds entirely to the exemplaryembodiment according to FIG. 16. Therefore, all the designations fromFIG. 16 are found in FIG. 24. Otherwise, reference is made to thecorresponding parts of the description.

[0183] Additional components in the exemplary embodiment according toFIG. 24 are a hydraulic accumulator 280, which may be, for example, apiston accumulator or a bubble accumulator and is designed for a lowpressure within a range of between 5 and 10 bar, and a 2/2-waydirectional seat valve 281, with which a fluid connection between thehydraulic accumulator 280 and the pressure space 35 can be controlled.In an off position of the valve 281, the fluid connection is shut off.By energizing an electromagnet 282, the valve 281 is brought into astraight-through position, so that a fluid exchange can take placebetween the hydraulic accumulator 280 and the pressure space 35. Theelectromagnet is in each case activated in parallel with theelectromagnetic clutch 195, as indicated by the common electrical switch283. The clutch 195 is actuated during the regulating movement, so thata temperature-induced volumetric change in the pressure fluid can becompensated for in each case during this movement. To build up the highlocking force, the clutch 195 is disengaged and the valve 281 is broughtinto the blocking position. No pressure fluid can now be displaced fromthe pressure space 35 into the hydraulic accumulator 280. The entiretravel of the small piston 28 is used for compressing the pressure fluidlocated in the pressure space 35.

[0184] The screw spindle 25 also passes through the hydraulic unit 12 inthe exemplary embodiment according to FIG. 25. The screw spindle 25 isin engagement with a spindle nut 253 which is formed as a recirculatingball sleeve and which, as indicated, has a spherical outer surface andcarries on the latter the armature plate 203 of an electromagneticclutch 195, this armature plate 203 being complemented radially on theinside to form a multi-piece cup. The spindle nut and the cup arelocated essentially in a central passage of a yoke disk 267, in front ofone end face of which the armature plate 203 lies and which accommodatesthe coil 198 in an annular groove 199 open axially toward the armatureplate.

[0185] The yoke disk 267 belongs to an intermediate part 287 of thehydraulic unit 12, this intermediate part 287, in the same way as theexemplary embodiments according to FIGS. 16, 19, 20, 21, 22 and 24,having an inner dimensionally stable tube 94 and a thin-walled outertube 92 surrounding the tube 94. The tube 92 is surrounded on theoutside by a plurality of individual brake rods 196 which, when restingon the relieved tube 92, complement one another to form a closed ringand which are overlapped by two annular disks 288 and 289, which arescrewed onto the end faces of the tube 94, and are held axially betweenthe two annular disks with slight play which permits their free mobilityin the radial direction. Again located between the tubes 92 and 94 isthe annular admission space 183, which is fluidically connected to thepressure space 35 via holes 98 running through the tube 94.

[0186] The yoke disk 267 is inserted into the tube 94 at its one endface and is screwed to this tube. At an axial distance from the yokedisk 267, an inner flange is formed in one piece with the tube 94, thisinner flange corresponding in its function to the cylinder base 38 ofthe exemplary embodiment according to FIG. 22 and therefore beingprovided with the same designation. The inner flange 38 is set backslightly relative to the one end face of the tube 94. With its outermargin, an annular diaphragm 290 is fastened to the annular disk 289screwed onto said end face, this annular diaphragm 290, at its innermargin, being fastened axially to the outer collar of a collar bush 291.The annular diaphragm is made of a high-grade steel. It forms the largepiston of the hydraulic unit 12 and, together with its intermediate part287 and the small piston, it encloses the essentially annular pressurespace 35.

[0187] To seal off the pressure space 35 to the outside, a seal 292 isfirst of all inserted between the annular diaphragm 290 and the annulardisk 289. Furthermore, a seal, to be precise a gasket, is also locatedbetween the outer collar of the bush 291 and the annular diaphragm. Aseal is of course also provided between the tube 94 and the annular disk289, even if this is not shown in any more detail. Serving to provide aseal between the bush 291 and the inner flange 38 is an arrangement oftwo further metallic annular sealing diaphragms 294 and 295, of whichthe sealing diaphragm 294, with its inner margin, is clamped in placebetween the gasket referred to and the outer collar of the bush 291. Theother sealing diaphragm 295 is fastened at its inner margin to the innerflange 38 with a clamping ring 296, there being a seal 297 between theinner flange 38 and the sealing diaphragm 295. At their outer margins,the two sealing diaphragms are connected to one another via two outerclamping rings 298 and an intermediate ring 299 lying between them, aseal 300 being located between the intermediate ring and each sealingdiaphragm. The pressure space 35 is therefore sealed off from the spacebetween the two sealing diaphragms 294 and 295 and thus from the gap,which changes in size during operation, between the bush 291 and theclamping ring 296 and from the atmosphere.

[0188] The small piston of the exemplary embodiment according to FIG.25, as in the exemplary embodiment according to FIG. 22, is formed by aplurality of little pistons 256 which are at the same angular distancesfrom one another and are guided in guide bushes 301 inserted into theinner flange 38 and projecting beyond the inner flange in the directionof the armature plate 203. The guide bushes result in a large guidanceand sealing length for the little pistons 256. In addition, the bushes301 serve as guides for compression springs 302, of which each issupported on the inner flange 38 and via a spring plate 303 on a littlepiston 256, and the little piston remains in contact with the armatureplate 203.

[0189] The hydraulic unit 12 of the exemplary embodiment according toFIG. 26, which is shown in a highly schematic form, is constructed so asto be double-acting inasmuch as power transmission in two oppositedirections is possible with it. The hydraulic unit has, as intermediatepart, a cylinder 317 which is symmetrical relative to a center radialplane and has two inner flanges 38 and 40 at a distance from the two endfaces of a dimensionally stable cylinder tube 94. The space between thetwo inner flanges is divided axially by a piston collar 319 of the largepiston 318 into two annular spaces 320 and 321 which are each part of apressure space 35.

[0190] Via a check valve 316 which can be opened by pilot control in amanner not shown in any more detail, each sectional space 320, 321 canbe connected to the clearance space 183 which exists between thedimensionally stable cylinder tube 94 and the deformable outer tube 92,on the outside of which the brake rods 196 are located.

[0191] The large piston 318 is a synchronous piston with two piston rods322 and 323 projecting away from the piston collar 319 on opposite sidesand directed outward through the inner flanges. Each piston rod issurrounded by a preloaded helical compression spring 324 which issupported, on the one side, on a spring plate 325 which can bear bothagainst a shoulder 326, pointing away from the piston collar 319, of thepiston rod and against the outer end face of an inner flange. Thedistance between the two shoulders 326 on the two piston rods is exactlythe same size as the distance between the two outer end faces of the twoinner flanges. On the other side, each helical compression spring 324 issupported on the corresponding piston rod via a spring plate 327 and asnap ring 328. In this way, the cylinder 317 is centered in a centerposition relative to the large piston 318 by the helical compressionsprings 324, as long as no force exceeding the preloading of a spring isacting.

[0192] The large piston 318 has a circular-cylindrical cavity 332 whichlies with its axis in the axis of the piston and at whose two end facescentral passages 333, the diameter of which is smaller than the diameterof the cavity 332, lead outward. A small piston 334 of the hydraulicunit 12 is located in the cavity 332 and in the passages 333, and thissmall piston 334, with a piston collar 335, divides the cavity 332 intotwo small sectional spaces 336 and 337, of which the one sectional space336, via a fluid path 338 running through the large piston 318, isfluidically connected to the sectional space 320 of substantially largercross section and the sectional space 337, via a fluid path 339, isfluidically connected to the sectional space 321 of substantially largercross section at the piston collar 319 of the large piston 318. Thesectional spaces connected to one another and the corresponding fluidpath in each case form a pressure space 35. Starting from the pistoncollar 335 on each side of the same is a piston rod 340 or 341,respectively, which emerges outward through the passage 333. In a mannernot shown in any more detail, the piston rod 340 is coupled to a driveelement, for example a screw spindle, which can be moved axially inopposite directions by an electric motor.

[0193] The other piston rod 341 has an outer shoulder 342 which pointsaway from the piston collar 335 and from which a guide and supportingmandrel 343 for a helical compression spring 344 extends and which liesin the plane of the end face 345 of the piston rod 322 of the largepiston 318 when the piston collar 335 of the small piston 334 is locatedcentrally in the cavity 337. An annular groove 199 in the end face 345accommodates the coil 198 of an electromagnetically actuable clutch 195.The latter also includes an armature plate 203 which surrounds themandrel 343 of the piston rod 341 and is loaded in the direction of theouter shoulder 342 and the end face 345 by the spring 344 supported onthe mandrel 343.

[0194] In FIG. 26, the hydraulic unit 12 is shown in a state in whichthe mold of an injection molding machine for plastics is completelyopen. The large piston 318 is centered relative to the cylinder 317 bythe springs 324. The small piston 334 assumes a central positionrelative to the large piston 318 in which the armature plate 203 islocated at the outer shoulder 342 and at the end face 345 of the largepiston. If the mold is now to be closed, the coil 198 is energized, thatis to say the clutch 195 is engaged, and the small piston 334 is movedto the right in the view according to FIG. 26 by appropriate activationof the electric motor (not shown). Via the armature plate 203, the largepiston 318 is carried along synchronously and thus the movable platenfastened to the large piston is moved. The large piston 318 also carriesalong the cylinder 37 via the left-hand helical compression spring 324in the figure. The pressure in the pressure spaces 35 does not change.

[0195] If the mold has finally been closed, a high resistance opposesthe further movement of the large piston 318. The coil 198 isde-energized. The small piston 334 continues to move in the directionfor reducing the small sectional space 337. As a result, the pressure inthe corresponding pressure space 35 increases and, via the one checkvalve 316, the pressure in the clearance space 183 also increases. Firstof all, the preloaded left-hand helical compression spring 324 stillprevents the cylinder 317 from giving way to the left. Finally, byfurther pressure increase in the pressure space 35, the outer tube 92 iswidened, so that the brake rods 196 abut on the inside against the wallof the bore 9. The cylinder 37 is then held by clamping in the bore 9,and the pressure in the pressure space 35 can be increased further byfurther movement of the small piston 334, so that the preloading forceof the left-hand helical compression spring 324 is overcome and the highlocking force for the mold is built up.

[0196] To open the mold, for which purpose a relatively high openingforce is now necessary to begin with, the electric motor is driven inthe opposite rotary direction, so that the small piston 334, as viewedaccording to FIG. 26, moves to the left, while the large piston 318remains in its position. By the movement of the piston 334 relative tothe piston 318, the small sectional space 337 is enlarged and thepressure in the corresponding pressure space 35 is reduced. The armatureplate 203 passes again to the end face 345 of the large piston 318. Thestate shown in FIG. 26 is achieved again.

[0197] The small piston 334 is moved further to the left and as a resulta pressure is built up in the other pressure space 35, this pressurefinally producing a force at the large piston which is sufficient foropening the mold. While the small piston moves relative to the largepiston, the helical compression spring 344 is loaded to a greaterextent, since its one end is carried along by the small piston, whereasthe other end is supported via the armature plate 203 on the static,large piston. If the mold has been opened, the large piston, on accountof the helical compression spring 344, follows the small piston untilthe armature plate 203 bears against the outer shoulder 342. The twopistons are subsequently moved together. A pressure drop in the onepressure space 35 having the sectional space 320 indicates that the moldhas opened. After the mold has opened, the clearance space 183 isrelieved of pressure, so that the cylinder 317 is centered relative tothe large piston 318 and is subsequently moved to the left together withthe pistons.

[0198] In the exemplary embodiment shown, two pilot-operated checkvalves 316 are provided for the admission of pressure to the clearancespace. In order to be able to exert the high locking force, pressure isapplied to the clearance space from the large sectional space 321 viathe one check valve. After the molding operation, the check valve isopened by pilot control, so that, with the drop in the pressure in thesectional space 321 resulting from the movement of the small piston 334to the left, the pressure in the clearance space 183 is also reduced andthe cylinder 317 is centered relative to the large piston 318. Duringthe subsequent pressure build-up in the large sectional space 320,pressure is also admitted again to the clearance space 183 via the othercheck valve and as a result the cylinder 317 is clamped in place again.After the mold has been opened, the check valve is opened by pilotcontrol.

[0199] In a variant, it is also possible for only the one check valve tobe provided between the large sectional space 321 and the clearancespace 183. This check valve is not opened until after the mold has beenopened, so that the cylinder remains clamped in place withoutinterruption from the start of the locking until after the opening ofthe mold.

[0200] While pressure is being built up in the one pressure space 35 bythe movement of the small piston relative to the large piston, in orderto avoid a vacuum arising in the other pressure space 35, it isconceivable to connect each pressure space to a hydraulic accumulatoraccording to the exemplary embodiment according to FIG. 22 or theexemplary embodiment according to FIG. 24. It is also conceivable toprestress the two pressure spaces to equally high pressures, so that,during a relative movement between the two pistons, the pressure in theone pressure space increases and the pressure in the other pressurespace drops, although not below atmospheric pressure. In this case,external admission of pressure to the clearance space according to theexemplary embodiment according to FIG. 20 appears favorable.

[0201] In FIGS. 27 to 31, a drive device according to the inventionconstructed in each case in principle like the exemplary embodimentaccording to FIG. 22 is supplemented by a purely electromechanical drivedevice 400 for actuating one or more ejectors for the molding. Thecomponents of this drive device are located on the piston rod 42 of thelarge piston 36 and on the movable platen 401, which forms a motion unitwith the large piston.

[0202] In the exemplary embodiment according to FIG. 27, a spindle nut403 is rotatably mounted in the piston rod 42 via rolling-contactbearings 402, this spindle nut 403 having a toothed driving wheel 404,via which it can be rotationally driven via a driving belt 405 by anelectric motor 406 which is fastened to the platen and can be reversedin its direction of rotation. Extending through the spindle nut is ascrew spindle 407 which is locked against rotation and to which anejector pin 408 passing through the platen is fastened. The ejector pin408 is moved to and fro by rotation of the electric motor 406 inopposite directions.

[0203] In the exemplary embodiment according to FIGS. 28 and 29, aplurality of ejector pins 408 are located on a plate 410, into whichthree spindle nuts 403 are inserted in a rotationally locked manner.Passing through each spindle nut is a screw spindle 407 which isrotatably mounted and held in place axially in a rolling-contact bearing402 fastened on the outside to the piston rod 42 and which carries atoothed driving wheel 404 in a rotationially locked manner between therolling-contact bearing and the plate 410. Again fastened to the platen401 is an electric motor 406 which, via a pinion sitting on its shaftand via a driving belt 405 placed around this pinion and the threedriving wheels 404, can drive the screw spindle 407 in a rotary mannerand, as a result, depending on the direction of rotation, can move theplate 410 and with the latter the three ejector pins 408 to and fro.

[0204] There is a discrepancy between the two FIGS. 28 and 29 withregard to the arrangement of one screw spindle 407, which in FIG. 28 isdepicted rotated through 90 degrees relative to FIG. 29 in order to beable to show a plurality of screw spindles in FIG. 28.

[0205] In the exemplary embodiment according to FIGS. 30 and 31, thedrive device 400 for a plurality of ejector pins 408 has a slider-crankmechanism with a sliding body 411, to which the ejector pins 408 arefastened and which is guided in the axial direction of the piston rodand of the screw spindle 25 and in the direction of movement of theplaten 401 in an adapter piece 412 attached to the piston rod 42 andconnected to the platen 401. Fastened to an extended motor shaft 413 ofan electric motor 406 held vertically on the platen 401 is a crank 414which is connected to the sliding body 411 in an articulated manner viaa coupling rod 415. The sliding body 411 and the ejector pins 408 aremoved forward and backward by rotation of the motor shaft 413 in twoopposite directions. So that the ejector pins do not have to be toolong, the articulation point of the coupling rod 415 is sunk in thesliding body 411 and the necessary recesses are made in the latter inorder not to hit the motor shaft, the crank and the coupling rod.

[0206] The exemplary embodiment according to FIG. 32 has a powertransmission means 12 with a cylinder 37 which, in its configurationwith the base 38, the flange 40 and the tubes 94 and 92, the clearancespace 183 in between and the brake rods 196, corresponds to the cylinder37 from FIG. 16.

[0207] The large piston 36, only schematically shown, has apiston-rod-like part 182, which is of smaller diameter and emergesoutward through the flange 40, and a piston-collar-like part 181, whichis of larger diameter and serves to guide the piston and seal off thepressure space 35. A helical compression spring 60 is again secured inposition between the piston 36 and the cylinder 37.

[0208] Like the piston 36 from FIG. 16, the piston 36 of the exemplaryembodiment according to FIG. 32 also has, in the interior, a cavity(clutch space) 186, which accommodates a coupling device 180 forcoupling the two pistons 36 and 28. The small piston 28, with a certaindiameter, enters the pressure space 35 in a sealed-off manner throughthe base 38 of the cylinder 37. Its cross section is reduced therein ina step 201, following which is a piston extension 202 of smallerdiameter. After crossing a blind hole 56 of the piston 36, this blindhole 36 being open toward the base 38 of the cylinder 37 and itsdiameter being so large that the piston 28 can plunge into it with itslarger diameter, the piston extension 202 enters the clutch space 186 ina sealed-off manner. In the latter, the small piston 28 is reduced onceagain in diameter and, with a pump piston section 420 of smallerdiameter compared with the extension 202, plunges in a sealing mannerinto an axial blind hole 421 starting from the clutch space 186. Thepump piston section 420 and the blind hole 421 form the displacementmeans and the displacement space of a simple plunger pump. Pressurefluid can flow to the blind hole 421 from a low-pressure accumulator 423via a check valve 422 opening toward the blind hole 421. Via a checkvalve 424 blocking flow toward the blind hole, pressure fluid can bedisplaced from the blind hole into a high-pressure accumulator 425.

[0209] Inside the clutch space 186, the cross-sectional area of which issubstantially larger than the cross-sectional area of the pistonextension 202 or of the pump piston section 420 of the small piston 28,the piston 28, at the transition from the extension 202 to the pumppiston section 420, carries a piston disk 188 which divides the clutchspace 186 into two spaces 426 and 427 sealed off from one another. Thespace 427 (air space) on the side of the extension 202 is open to theatmosphere, that is to say it is filled with air. The other space 426(fluid space) is filled with pressure fluid and is connected to anelectromagnetically actuable 3/2-way directional control valve 428 whichfluidically connects the fluid space 426 to the high-pressureaccumulator 425 in the off position and to the low-pressure accumulator423 in the actuated position. Inserted between the two hydraulicaccumulators is a spill valve 429 which opens from the high-pressureaccumulator to the low-pressure accumulator if a certain pressuredifference between the two hydraulic accumulators is exceeded.

[0210] In FIG. 32, the hydraulic unit is shown in a state in which themold of an injection molding machine for plastics is completely open.The large piston 36, with its end face 184, is located at the base 38 ofthe cylinder 37 via short spacers. The small piston 28 assumes aposition in which the piston disk 188 is located at the end of theclutch space 186. The directional control valve is in its off position,so that pressure is applied in the fluid space 426. This pressure is sohigh that the pressure fluid transmits the force required for theregulating movement of the movable platen like a rigid mechanism. If themold is now to be closed, the small piston 28 and with it the pistondisk 188 are moved to the right in the view according to FIG. 32 byappropriate activation of the electric motor (not shown in FIG. 32). Themovement of the piston disk, via the pressure fluid in the fluid space426, is transmitted directly to the large piston 36 and thus to themovable platen. The large piston 36 also carries along the cylinder 37via the helical compression spring 60. The pressure in the pressurespace 35 does not change.

[0211] If the mold has finally been closed, the directional controlvalve 428 is changed over, so that the pressure fluid in the fluid space426 expands to a low pressure and, during the further movement of thesmall piston 28 relative to the large piston 36, can be displaced withlittle force from the fluid space 426 into the low-pressure accumulator423. The piston 28 continues to move and plunges deeper into the blindhole 56 and displaces pressure fluid with its annular surface 201. As aresult, the pressure in the pressure space 35 increases, so that thecylinder 37 is clamped in place and the high locking force is built up.

[0212] During the further movement of the small piston 28, its pumppiston section 420 plunges deeper into the blind hole 421 and displacespressure fluid from it into the high-pressure accumulator 425. Thedisplaced quantity is slightly larger than the quantity which has flowedaway into the low-pressure accumulator 423 during the precedingdecompression of the fluid space 426 and which will flow from thehigh-pressure accumulator into the fluid space during the subsequentcompression. The excess quantity is kept as small as possible and passesfrom the high-pressure accumulator via the spill valve 429 into thelow-pressure accumulator again, so that the pressure difference betweenthe two accumulators does not exceed a certain value.

[0213] To open the mold, the electric motor is driven in the oppositerotary direction, so that the piston 28, as viewed according to FIG. 32,moves to the left. Pressure fluid flows from the low-pressureaccumulator 423 via the directional control valve 428 into the expandingfluid space 426 and via the check valve 422 into the expandingdisplacement space 421. The pressure in the pressure space 35 isreduced. Finally, the piston 28, via the piston disk 188, carries alongthe piston 36 and the latter carries along the cylinder 37 in theopening direction of the mold. The directional control valve is broughtinto its off position again and as a result the high pressure prevailingin the hydraulic accumulator 425 is applied to the fluid space 426.

[0214] Of the exemplary embodiment according to FIG. 33, only the onehalf produced by dividing along the direction of movement of a movableplaten is shown. The other half is constructed in mirror image thereto.

[0215] Fastened in a fixed platen 433 outside the center axis 434 is anelectric hollow-shaft motor 11, the hollow shaft of which has arecirculating ball screw 21 on the inside and is in engagement via balls24 with a threaded section 27 of a rectilinearly movable stroke spindle25 locked against rotation. From the threaded section 27, a piston rod340 of the small piston 334 of a hydraulic power transmission means 12extends parallel to the center axis right into a cylindrical cavity 435of a plate-shaped intermediate part 437 of the power transmission means12, this plate-shaped intermediate part 437, in a manner not shown inany more detail, being guided on spars along the axis 434. Fastenedinside the cavity 435 to the piston rod 340 is a piston collar 335,which, on the piston-rod side, defines a sectional space 337, filledwith pressure fluid, of a pressure space 35 of the power transmissionmeans and, on the side remote from the piston rod, is exposed to theatmosphere.

[0216] Before entry to the cavity 435, the piston rod 340 crosses aclutch space 186 which is located in the plate 437 and in which thepiston disk 188 of a hydraulic coupling device 180 is fastened to thepiston rod. As in the exemplary embodiment according to FIG. 32, thepiston disk divides the clutch space 186 into two clutch sectionalspaces 426 and 427 sealed off from one another. The clutch sectionalspace 427 situated toward the cavity 435 is permanently connected to alow-pressure accumulator 423 sitting on the plate 437. The other clutchsectional space 426, as in the exemplary embodiment according to FIG.32, is filled with pressure fluid and connected to anelectromagnetically actuable 3/2-way directional control valve 428 whichfluidically connects the clutch sectional space 426 to the high-pressureaccumulator 425 in the off position and to the low-pressure accumulator423 in the actuated position. The clutch sectional spaces at the othersmall piston 334 are connected in the same way to the directionalcontrol valve 428 and the low-pressure accumulator 423. As in theexemplary embodiment according to FIG. 32, there is a pumpingarrangement (not shown in any more detail) which delivers pressure fluidfrom the low-pressure accumulator to the high-pressure accumulator inorder to compensate for the entrainment of pressure fluid by thepressure build-up and pressure reduction in the space 426 and forleakage via the piston disk 188.

[0217] The plate 437 accommodates the large piston 36 of the powertransmission means 12 concentrically to the center axis 434. The largepiston 36, with the plate 437, defines a sectional space 321 of thepressure space 35, this sectional space 321 being fluidically connectedto the sectional space 337 at the small piston 334 via a passage 438leading through the plate. Secured in position between the large piston36 and the plate 437 is a helical compression spring 60 which loads bothparts in the direction for minimizing the volume of the sectional space321.

[0218] Fastened to the plate 437 are rods 439, with which the plate canbe locked relative to the fixed platen 433, that is against movement.

[0219] The mold for the plastic part to be injection molded can becarried by the large piston 36 directly or via an additional platen.

[0220] In FIG. 33, the drive device is shown in a state in which themold of an injection molding machine for plastics is completely open.The large piston 36 of the hydraulic unit 12, with its end face 184, islocated at the base of the receptacle in the plate 437 via shortspacers. The small piston 334 assumes a position in which the pistondisk 188 is located at the end of the clutch space 186 and the pistoncollar 335 makes the sectional space 337 the maximum size. Thedirectional control valve is located in its off position, so thatpressure is applied in the clutch sectional space 426. This pressure isso high that the pressure fluid transmits the force required for theregulating movement of the movable mold half like a rigid mechanism. Ifthe mold is now to be closed, the small piston 334 and with it thepiston disk 188 are moved to the right in the view according to FIG. 33by appropriate activation of the electric motor 11. The movement of thepiston disk, via the pressure fluid in the clutch sectional space 426,is transmitted directly to the plate 437, that is to the intermediatepart of the power transmission means 12, and from the intermediate partto the large piston 36 and thus to the movable mold half. The pressurein the pressure space 35 does not change.

[0221] If the mold has finally been closed, the plate 437 is locked viathe rods 439 and the directional control valve 428 is changed over. Thepressure fluid in the clutch sectional space 426 expands to a lowpressure and, during the further movement of the small piston 334relative to the plate 437, can be displaced from the clutch sectionalspace 426 into the low-pressure accumulator 423 by the piston disk 188.The piston 334 continues to move and, with its piston collar 335,reduces the volume of the sectional space 337 of the pressure space 35.As a result, the pressure in the pressure space 35 increases, so thatthe high locking force is built up.

[0222] To open the mold, the electric motor 11 is driven in the oppositerotary direction, so that the piston 334, as viewed according to FIG.33, moves to the left. The pressure in the pressure space 35 is reduced.Pressure fluid flows from the low-pressure accumulator 423 via thedirectional control valve 428 into the expanding clutch sectional space426. The locking of the plate 437 is then neutralized. The plate 437 issubsequently carried along by the small piston 334 via the piston disk188, and the piston 36 is carried along by the plate 437 via the helicalcompression spring 60 preloaded in accordance with the force requiredfor the regulating movement. The directional control valve is broughtinto its off position again and as a result the high pressure prevailingin the hydraulic accumulator 425 is applied to the fluid space 426.

[0223] In the two exemplary embodiments according to FIGS. 34 and 35,the hydraulic power transmission means 12 is of double-actingconstruction. In the fixed platen 433, two spindle nuts 253 arerotatably mounted axially in a fixed position diametrically opposite oneanother relative to the center axis 434 via self-aligning rollerbearings 445, these spindle nuts 253 having a driving disk 446, viawhich they can be driven via a belt by an electric motor (not shown inany more detail). Each spindle nut 253 is in engagement via balls with athreaded section 27 of a rectilinearly movable stroke spindle 25 lockedagainst rotation. As in the exemplary embodiment according to FIG. 33,from the threaded section 27 of the stroke spindle 25, a piston rod 340of a small piston 334 of a hydraulic power transmission means 12 extendsparallel to the center axis 434 in a sealed-off manner through a passage447 right into a cavity 448, having a plurality of cylindrical sectionsdiffering from one another in their diameters, of a plate-shapedintermediate part 437 of the power transmission means 12, thisplate-shaped intermediate part 437, in a manner not shown in any moredetail, being longitudinally guided on spars. Following the passage 447is first of all a cavity section 449, the diameter of which is aboutthree times as large as the diameter of the piston rod 340. Thefollowing cavity section 450 has a larger diameter than the cavitysection 449. The diameter of the adjoining cavity section 451 liesbetween the diameters of the sections 449 and 450. Finally, the diameterof the last, blind-hole-like cavity section 452 is slightly smaller thanthe diameter of the passage 447. The small piston 334, with aplunger-like piston section 455, plunges in a sealed-off manner into thecavity section 452. At the transition between the piston rod 456 and thepiston section 455, a driving disk 456 is fastened to the latter, thediameter of this driving disk 456 being smaller than the diameter of thecavity section 451. In front of the driving disk, a further, steppedpiston section 457 is longitudinally guided on the piston rod 340. Thispiston section 457 plunges in a sealed-off manner into the cavitysection 449 and has an additional piston collar 458 which constitutes afurther piston section of the small piston 334. The piston collar 458has a diameter which is slightly smaller than the diameter of the cavitysection 450 and is sealed off relative to the wall of this cavitysection. Secured in position between the piston section 457 and thepiston rod 340 is a compression spring 459 which loads the pistonsection in the direction of the driving disk 456 and in the direction ofthe step between the two cavity sections 450 and 451. The step forms astop 460 for the piston section 457.

[0224] The plate 437 accommodates the large piston 36 of the powertransmission means 12 concentrically to the center axis 434. The largepiston 36 is now formed so as to be double-acting as a differentialpiston with a piston collar 310 and a piston rod 322 and defines, withthe plate 437, a fully cylindrical sectional space 321 of a firstpressure space 35, the admission of pressure to which results in thelarge piston being loaded in the extension direction of the piston rod,and an annular sectional space 320 of a second pressure space 35. Theplate and the large piston are centered relative to one another in aspring-loaded manner by two helical compression springs 461 and 462which surround the piston rod 322 and which are both supported on oneside on an annular spring plate 463, which can be carried along by theplate 437 and by the large piston 36, and on the other side on the largepiston and on the plate, respectively.

[0225] In both exemplary embodiments according to FIGS. 34 and 35, thesectional space 320 is permanently fluidically connected to theclearance space 464 in front of the piston sections 455 of the two smallpistons 334. Both exemplary embodiments again include a low-pressureaccumulator 423 and a high-pressure accumulator 425 and also a 3/2-waydirectional control valve 428. The clearance spaces 465 between the sealat the piston section 455 and the seal at the piston collar 458 arepermanently fluidically connected to the low-pressure accumulator 423.

[0226] A difference between the two exemplary embodiments justconsidered is the fluidic connection of the clearance spaces 456 betweenthe seal at the piston collars 458 and the seal, lying at the wall ofthe respective cavity section 449, of the piston section 457 and theclearance spaces 467 in front of the last-mentioned seal. In theexemplary embodiment according to FIG. 34, the clearance spaces 466 arepermanently connected to the sectional space 321 at the large piston 36and thus form sectional spaces of the first pressure space 35. Theclearance spaces 467, depending on the position of the directionalcontrol valve 428, are connected either to the low-pressure accumulatoror to the high-pressure accumulator. Together they form the clutch spaceof a hydraulic clutch device which is provided between the small piston334 and the plate 437, that is to say the intermediate part of thehydraulic power transmission means 12, and the clutch disk of which isthe smaller part of the piston section 457.

[0227] In the exemplary embodiment according to FIG. 35, the pistoncollars 458 correspond to the piston section 420 and the clearancespaces 466 correspond to the space 421 of the exemplary embodimentaccording to FIG. 32. Accordingly, pressure fluid can be displaced fromthese clearance spaces 466 via a check valve 424 into the high-pressureaccumulator 425 and can subsequently flow from the low-pressureaccumulator 423 via a check valve 422 into the clearance spaces 466.There is a 4/2-way directional control valve with an off position inwhich the clearance spaces 467 are connected to the high-pressureaccumulator 425 and the sectional space 321 of the first pressure space35 is connected to the low-pressure accumulator 423. The directionalcontrol valve can be brought by an electromagnet into the secondoperating position, in which the hydraulic accumulators are shut offtoward the spaces 321 and 467 and the sectional space 321 is connectedto the clearance spaces 467. In this respect, the latter are sectionalspaces of the first pressure space 35. The clearance spaces 467 at thesame time form the clutch space of a hydraulic clutch arranged betweenthe small piston 334 and the plate 437.

[0228] In FIGS. 34 and 35, the two drive devices are shown in a state inwhich the mold of an injection molding machine for plastics iscompletely open. The piston collar 319 of the large piston 36 of thehydraulic unit 12 is located in a center position relative to itspossible length of stroke. The piston sections 457 of the small pistons334 bear against the stop 460. The driving disk 456 is located justbehind the piston section 457. The directional control valve 428 or 475,respectively, is in its off position, so that pressure is applied in theclearance spaces 467. This pressure is so high that the pressure fluidtransmits the force required for the regulating movement of the movablemold half like a rigid mechanism. If the mold is now to be closed, thepiston rod 340 and, with the latter, the various sections of the smallpistons 334 are moved to the right in the view according to FIGS. 34 and35 by appropriate activation of the electric motor. The movement of thepiston section 457, via the pressure fluid in the clearance spaces 467,is transmitted directly to the plate 437, thus to the intermediate partof the power transmission means 12, and from the intermediate part viathe helical compression spring 461 to the large piston 36 and thus tothe movable mold half. The pressure in the pressure spaces 35 does notchange.

[0229] If the mold has finally been closed, the plate 437 is locked viathe rods 439. In the exemplary embodiment according to FIG. 34, thedirectional control valve 428 is changed over. The pressure fluid in theclearance spaces 467 expands to a low pressure and, during the furthermovement of the small pistons 334 relative to the plate 437, can bedisplaced from the clearance spaces 467 into the low-pressureaccumulator 423. The pistons 334 continue to move and, with the pistoncollars 458, reduce the volume of the sectional spaces 466 of the firstpressure space 35. As a result, the pressure in the sectional space 321of this pressure space 35 also increases, so that the high locking forceis built up.

[0230] In the exemplary embodiment according to FIG. 35, after thechangeover of the directional control valve 475, pressure fluid isdisplaced from the clearance spaces 467 into the sectional space 321 ofthe first pressure space 35 by the further movement of the small pistons334, so that a high locking pressure is likewise built up. During thefurther movement of the small pistons 334, their piston collars 458displace pressure fluid from the clearance spaces 466 into thehigh-pressure accumulator 425. As in the exemplary embodiment accordingto FIG. 32, the movement of the small pistons relative to a fixed partof the hydraulic power transmission means is thus used in order todeliver pressure fluid from the low-pressure accumulator into thehigh-pressure accumulator.

[0231] To open the mold, the small pistons 334, by reversing thedirection of rotation of the driving electric motor, are moved to theleft, as viewed according to FIGS. 34 and 35, in the course of which thepiston section 457 follows the piston rod 340 on account of the spring459. The pressure in the first pressure space 35 is reduced. In theexemplary embodiment according to FIG. 34, pressure fluid flows from thelow-pressure accumulator 423 via the directional control valve 428 intothe expanding clearance spaces 467 until the piston sections 457 bearagainst the stops 460. A pressure is subsequently built up by the pistonsections 455 of the small pistons 334 plunging into the clearance spaces464 in the second pressure space 35, this pressure releasing the movablemold half. The locking of the plate 437 is then neutralized. The springs459, the preloading of which has been further increased by the furthermovement of the small pistons to the left, push the plate 437 and thelarge piston 36 in such a way as to follow the small pistons. The plate437 and the large piston 36 then follow the small pistons 334 on accountof the springs 459 and the springs 462. The directional control valve isbrought into its off position again and as a result the high pressureprevailing in the hydraulic accumulator 425 is applied to the fluidspace 467.

[0232] In the exemplary embodiment according to FIG. 35, after reversalof the direction of movement of the small pistons 334, pressure fluidflows out of the low-pressure accumulator 423 via the check valve 422into the expanding clearance spaces 466. The first pressure space 35 isdecompressed by the movement of the piston sections 457 up to the stops460. The directional control valve 475 is then changed over into its offposition, so that the sectional spaces 467 are connected to thehigh-pressure accumulator and the sectional space 321 of the firstpressure space 35 is connected to the low-pressure accumulator. As inthe exemplary embodiment according to FIG. 34, a pressure issubsequently built up by the piston sections 455 of the small pistons334 plunging into the clearance spaces 464 in the second pressure space35, this pressure releasing the movable mold half. The locking of theplate 437 is then neutralized. The mold is then opened as in theexemplary embodiment according to FIG. 34.

1. A drive device, in particular for the closing unit, the injectionunit or the ejectors of an injection molding machine for plastics,having a drive element (25, 234, 253) which can be moved axially by anelectric motor (11, 170), and having a hydraulic unit (12) which can bemoved in the same direction as the drive element (25, 234, 253) bymoving the latter, characterized by the fact that the hydraulic unit(12) is a power transmission means having two pistons (28, 228, 256,334; 36, 290, 318), which are movable relative to one another and differfrom one another in the size of their effective areas, and having anintermediate part (37, 287, 317, 437) which together with the pistonsencloses a pressure space (35) filled with a pressure fluid, by the factthat the small piston (28, 228, 256, 334) having the smaller effectivearea is mechanically connected to the drive element (25, 234, 253), bythe fact that the hydraulic unit (12) can be moved as an entity for aregulating movement, and by the fact that, for exerting a high force bythe large piston (36, 290, 318) having the larger effective area, theintermediate part can be locked against displacement relative to a fixedframe (10, 240, 433).
 2. The drive device as claimed in claim 1,characterized by the fact that there is a coupling device (60, 324) withwhich the intermediate part (37, 287, 317) and the large piston (36,287, 318) of the hydraulic unit (12), for a regulating movement, arecoupled to one another in a fixed position, and by the fact that, forexerting the high force by the large piston (36, 318) of the hydraulicunit (12), the fixed coupling between large piston (36, 318) andintermediate part (37, 287, 317) can be released.
 3. The drive device asclaimed in claim 1 or 2, characterized by the fact that the couplingdevice comprises a spring (60, 324) which is secured in position betweenthe large piston (36, 318) and the intermediate part (37, 317).
 4. Thedrive device as claimed in claim 3, characterized by the fact that thelarge piston (36, 318) and the intermediate part (37, 317) can bepressed against one another axially by the spring (30, 324), and by thefact that, when the large piston (36, 318) and the intermediate part(37, 317) bear against one another, the preloading force of the spring(60, 324) is greater than the regulating force required for performingthe regulating movement.
 5. The drive device as claimed in claim 3 or 4,characterized by the fact that the inner part (36) of the two partscomprising the large piston (36) and the intermediate part (37) has anaxially open annular groove (57), and by the fact that the spring (60)is accommodated by the annular groove (57) and is supported on the baseof the annular groove (57).
 6. The drive device as claimed in apreceding claim, characterized by the fact that the intermediate part isformed as a cylinder (37) which surrounds the large piston (36) on theoutside, and by the fact that the small piston (28, 256) projectsplunger-like through a flange (38) of the cylinder (37) freely into thepressure space (35).
 7. The drive device as claimed in claim 6,characterized by the fact that the large piston (36) has a blind hole(56) which is open toward the flange (28) of the cylinder (37) and intowhich the small piston (28) can plunge.
 8. The drive device as claimedin claim 6 or 7, characterized by the fact that the large piston (36)has a piston rod (42), the diameter of which is smaller than the sealingdiameter of the large piston (36) relative to the cylinder (37) andwhich emerges from the cylinder (37) through a flange (40) of the latterwhich is opposite the flange (38).
 9. The drive device as claimed in apreceding claim, characterized by the fact that the inner part (36) ofthe two parts comprising the large piston (36) and the intermediate part(37) has two spaced-apart guidance points (47, 49) relative to theenvelope (43) of the outer part (37), the sectional space locatedaxially between the two guidance points (47, 49) being freely connectedto a sectional space on the one side of the inner part (36) and the twoparts (36, 37) bearing tightly against one another at one guidance point(49).
 10. The drive device as claimed in a preceding claim,characterized by the fact that the intermediate part and the largepiston can be coupled to one another in a positive-locking manner by thecoupling device, and by the fact that the coupling device is releasable.11. The drive device as claimed in a preceding claim, characterized bythe fact that there is a coupling device (85, 180, 195) with which thedrive element (25, 253) and the intermediate part (37, 287, 437) of thehydraulic unit (12) are directly coupled to one another in a fixedposition for a regulating movement, and by the fact that, for exertingthe high force by the large piston (36, 290) of the hydraulic unit (12),the fixed coupling between the drive element (25, 253) and theintermediate part (37, 287, 437) can be released.
 12. The drive deviceas claimed in claim 11, characterized by the fact that the large piston(36) and the intermediate part (37) of the hydraulic unit (12) can bepressed against one another by a spring (60), the preloading force ofwhich is lower than the regulating force required for performing theregulating movement.
 13. The drive device as claimed in a precedingclaim, characterized by the fact that there is a coupling device (180,195) with which the drive element (25, 234) or the small piston (28,228, 334), on the one hand, and the large piston (36, 318) of thehydraulic unit (12), on the other hand, are coupled directly to oneanother in a fixed position for a regulating movement, and by the factthat, for exerting the high force by the large piston (36, 318) of thehydraulic unit (12), the fixed coupling between the drive element (25,234) or the small piston (28, 228, 334) and the large piston (36, 318)can be released.
 14. The drive device as claimed in claim 13,characterized by the fact that the large piston (38, 318) and theintermediate part (37, 317) of the hydraulic unit (12) can be pressedagainst one another by a spring (60, 324), via which the intermediatepart (37, 317) can be carried along in the closing direction by thelarge piston (36, 318).
 15. The drive device as claimed in one of claims11 to 14, characterized by the fact that the coupling device (195) isan, in particular, electromagnetically actuable clutch which has a coil(198) located on one part (36, 37, 287) and an armature (203) which isheld on the other part (28, 228, 253) which, when current flows throughthe coil (198), is held axially on the latter.
 16. The drive device asclaimed in one of claims 11 to 14, characterized by the fact that thecoupling device (180) between the drive element or the small piston (28,334), on the one hand, and the intermediate part (437) or the largepiston (36), on the other hand, is a hydraulic clutch., in which casepressure fluid, during the regulating movement, is trapped in a clutchspace (186, 467) between the two parts (28, 36, 437) coupled to oneanother and can be displaced from the clutch space (186, 467) for movingthe two parts relative to one another.
 17. The drive device as claimedin one of claims 11 to 14, characterized by the fact that the couplingdevice (180) is an in particular hydraulic slip clutch.
 18. The drivedevice as claimed in claim 16 or 17, characterized by the fact that thedrive element or the small piston (28) enters a closed-off clutch space(186), filled with a fluid, of the intermediate part or of the largepiston (36) and carries, in the region of the clutch space (186), aseparating disk (188) separating said clutch space into two clutchsectional spaces, and by the fact that the two clutch sectional spacescan be fluidically connected to one another by a valve arrangement (189,190).
 19. The drive device as claimed in claim 18, characterized by thefact that the valve arrangement has two check valves (189, 190) in anantiparallel arrangement.
 20. The drive device as claimed in claim 19,characterized by the fact that the valve arrangement (189, 190) isaccommodated on the separating disk (188).
 21. The drive device asclaimed in one of claims 13 to 20, characterized by the fact that thelarge piston (36) has a clutch space (186), into which the drive elementor the small piston (28, 228) extends and in which the coupling device(180, 195) is located.
 22. The drive device as claimed in claim 21,characterized by the fact that the small piston (28) plunges in asealed-off manner across the clutch space (186) into a blind hole (56)of the large piston (36), this blind hole (56) forming a sectional spaceof the pressure space -(35) and being fluidically connected to asectional space of the pressure space (35) which adjoins a largeeffective area of the large piston (36).
 23. The drive device as claimedin claim 21., characterized by the fact that the small piston (28, 228)is a stepped piston with a section of larger diameter and a section(202) of smaller diameter following this section of larger diameter, bythe fact that the small piston (28, 228), with the section of largerdiameter, enters the pressure space (35) in a sealed-off manner and,with the section (202) of smaller diameter, enters the clutch space(186), so that the differential area between the two sections ofdifferent diameters forms the effective area of the small piston (28,228).
 24. The drive device as claimed in a preceding claim,characterized by the fact that the intermediate part (37, 287, 317) ofthe hydraulic unit (12) can be locked against displacement relative tothe fixed frame (10, 240) by friction grip with the fixed frame (10,240).
 25. The drive device as claimed in claim 24, characterized by thefact that the friction grip can be produced by hydraulically applyingpressure to the one friction-grip partner (92, 211).
 26. The drivedevice as claimed in claim 25, characterized by the fact that thepressure prevailing in the pressure space (35) can be applied to the onefriction-grip partner (92).
 27. The drive device as claimed in claim 26,characterized by the fact that pressure can be applied to the onefriction-grip partner (92, 211) by feeding external pressure medium. 28.The drive device as claimed in claim 27, characterized by the fact thatthe external pressure medium is delivered by a hydraulic pump (214)which is arranged in a closed hydraulic circuit with a hydraulicaccumulator (216) in the high-pressure branch and with a hydraulicaccumulator (215) in the low-pressure branch.
 29. The drive device asclaimed in one of claims 25 to 28, characterized by the fact that atleast one brake shoe (211), preferably a plurality of individual brakeshoes (211), to which pressure can be applied from outside and which canbe brought into contact with the intermediate part (37) toward theinside, are arranged in the frame.
 30. The drive device as claimed inone of claims 25 to 28, characterized by the fact that the intermediatepart (37) of the hydraulic unit (12) has a tube section (43, 92) whichcan be elastically extended radially outward by internal pressure forproducing a friction grip between the intermediate part and a wall of abore (9) of the fixed frame (10, 240).
 31. The drive device as claimedin claim 30, characterized by the fact that individual, radially movablebrake rods (196) are arranged around the extensible tube section (92) ofthin construction, these brake rods (196) lying axially with slight playbetween stops of the intermediate part (37, 287, 317).
 32. The drivedevice as claimed in claim 31, characterized by the fact that the brakerods (196) are provided with a friction lining (197) on the outside. 33.The drive device as claimed in one of claims 30 to 32, characterized bythe fact that the intermediate part (37, 287, 317) of the hydraulic unit(12) has a tube section (43, 92) which defines the pressure space (35)and which can be elastically extended radially outward by a pressure inthe pressure space (35) for producing a friction grip between theintermediate part and a wall of a bore (9) of the fixed frame (10). 34.The drive device as claimed in claim 33, characterized by the fact thatthe pressure space (35) is located between a first flange (38) of thecylinder (37) and the large piston (36), and by the fact that the largepiston (36) extends from a guidance and sealing point (47) between itand an extensible tube section (43) of the cylinder (37) toward thefirst flange (38) and, closer to the first flange (38), has the base ofthe annular groove (57) for the spring (60) and, if need be, a secondguidance point (49).
 35. The drive device as claimed in one of claims 30to 34, characterized by the fact that the intermediate part (37, 287,317) has a dimensionally stable inner tube section (94), in which thelarge piston (36) is guided in a sealed-off manner, and an outer tubesection (92) which surrounds the inner tube section (94) while forming aclearance space (96, 97, 183), by the fact that pressure can be appliedto the clearance space, and by the fact that the outer tube section (92)can be extended radially outward by pressure applied in the clearancespace (96, 97, 183).
 36. The drive device as claimed in claim 35,characterized by the fact that the clearance space (96, 97, 183) isfluidically connected to the pressure space (35) via at least oneconnecting passage (98), and the pressure applied in the pressure space(35) can be applied to the outer tube section (92).
 37. The drive deviceas claimed in claim 35 or 36, characterized by the fact that a spiralgroove (97), to which pressure medium can be fed, is formed in one ofthe surfaces, radially opposite one another, of an inner and an outertube section (94, 92), preferably in the surface of the inner tubesection (94), and by the fact that the outer tube section (92) rests onthe inner tube section (94) when no pressure is applied or when slightpressure is applied.
 38. The drive device as claimed in one of claims 24to 28, characterized by the fact that first metal sheets (77) arefastened to the intermediate part (37) of the hydraulic unit (12) andsecond metal sheets (78) are fastened to the fixed frame (10), and thesemetal sheets (77, 78) interlock and can be pressed against one anotherfor locking the intermediate part (37) of the hydraulic unit (12). 39.The drive device as claimed in one of claims 24 to 28, characterized bythe fact that the intermediate part (37) of the hydraulic unit (12) canbe locked against displacement relative to the fixed frame (10) byclamping wedges (111, 117).
 40. The drive device as claimed in claim 39,characterized by the fact that there is a first clamping wedge (117)which is arranged so as to be axially fixed and radially movablerelative to the intermediate part (37), and by the fact that a secondclamping wedge (111) interacting with the first clamping wedge (117) isaxially displaceable.
 41. The drive device as claimed in claim 40,characterized by the fact that the two clamping wedges (111, 117) arearranged on the intermediate part (37).
 42. The drive device as claimedin claim 41, characterized by the fact that the second clamping wedge(111) is hydraulically displaceable in the one direction.
 43. The drivedevice as claimed in claim 42, characterized by the fact that the secondclamping wedge (111) is displaceable for clamping the intermediate part(37) via a piston (113), to which the pressure prevailing in thepressure space (35) can be applied.
 44. The drive device as claimed inclaim 40, 41 or 42, characterized by the fact that the second clampingwedge (111) is displaceable in the one direction by a spring forceindependently of the pressure in the pressure space (35).
 45. The drivedevice as claimed in one of claims 39 to 44, characterized by the factthat the intermediate part (37) can be clamped to the frame (10) byclamping the clamping wedges (111, 117) in a bore (9) of a machine partfixed to the frame.
 46. The drive device as claimed in one of claims 39to 44, characterized by the fact that the intermediate part (37) can beclamped to the frame (10) by clamping the clamping wedges (111, 117) tospars (124) of the frame (10).
 47. The drive device as claimed in one ofclaims 1 to 23, characterized by the fact that the intermediate part(37) can be locked relative to the fixed frame (10) by trapping apressure fluid volume in a second pressure space (0.129), the volume ofwhich changes when the intermediate part (37) is moved and which can beconnected to a supply reservoir (131) for the pressure fluid and can beshut off from the supply reservoir (131) by a valve arrangement (132,133).
 48. The drive device as claimed in claim 47, characterized by thefact that the second pressure space (129) directly adjoins theintermediate part (37) and, in the direction of movement, -'s locatedopposite the first pressure space (37) in such a way as to be separatedfrom the latter by a wall (38) of the intermediate part (37).
 49. Thedrive device as claimed in one of claims 1 to 23, characterized by thefact that the intermediate part (37) of the hydraulic unit (12) can belocked against a displacement relative to the fixed frame by positivelocking with the fixed frame (10).
 50. The drive device as claimed inclaim 49, characterized by the fact that the intermediate part (37) canbe locked by a plurality of locking elements (76) which are arrangedaround it at equal distances apart and which can be moved radiallyinward in front of a stop wall of the intermediate part (37).
 51. Thedrive device as claimed in claim 50, characterized by the fact that eachlocking element (76) is pivotable about an axis parallel to the axis ofthe hydraulic unit (12).
 52. The drive device as claimed in claim 50 or51, characterized by the fact that the locking elements (76) can be setin their axial position.
 53. The drive device as claimed in one ofclaims 1 to 23, characterized by the fact that the intermediate part(37) can be locked by an axial stop (149, 160, 174) which can be movedin accordance with the regulating movement of the intermediate part(37), the force chain for axially supporting the intermediate part (37)comprising a self-locking screw drive (144, 148; 156, 161).
 54. Thedrive device as claimed in claim 53, characterized by the fact that theaxial stop (149), via a clutch or a slip clutch (142), can be moved byan electric motor (11), in particular by the same electric motor (11)with which the drive element (25) can also be driven, the clutch (142)being located in the force chain between the electric motor (11) and thescrew drive (144, 148).
 55. The drive device as claimed in claim 54,characterized by the fact that the clutch is a slip clutch (142), and bythe fact that there is a brake (150) with which a secondary-side part(145) of the slip clutch (142) can be locked.
 56. The drive device asclaimed in claim 54 or 55, characterized by the fact that the driveelement is a screw spindle (25), the thread (27) of which is inengagement with a rotating output part (19) of the electric motor (11),and by the fact that the axial stop (149) can be moved via the rotatingoutput part (19) and the clutch (142).
 57. The drive device as claimedin claims 53 to 56, characterized by the fact that the axial stop (160,174) can be moved by a second electric motor (163).
 58. The drive deviceas claimed in one of claims 53 to 57, characterized by the fact that thestop (149, 160) can be moved after and ahead of the intermediate part(37) in its direction of movement via a force chain in which theself-locking screw drive (144, 148; 156, 161) is located.
 59. The drivedevice as claimed in one of claims 53 to 57, characterized by the factthat a rotationally drivable part (174) of the screw drive (144, 148)meshes directly with a section (177), provided with a thread (148), ofthe intermediate part (173) and constitutes the stop.
 60. The drivedevice as claimed in a preceding claim, characterized by the fact thatcooling passages leading through the hydraulic unit (12) are providedfor dissipating heat from the pressure fluid.
 61. The drive device asclaimed in a preceding claim, characterized by the fact that theelectric motor is an electric linear motor.
 62. The drive device asclaimed in a preceding claim, characterized by the fact that the smallpiston (228) of the hydraulic unit (12) is formed as a hollow piston, bythe fact that a screw spindle (25) arranged in an axially fixed positioncan be rotationally driven by the electric motor (11), by the fact thatthe screw spindle (25) is accommodated by the hollow small piston (228),and by the fact that the small piston (228) comprises a spindle nut(234) which is in engagement with the screw spindle (25) over the entirestroke and is locked against rotation.
 63. The drive device as claimedin claim 62, characterized by the fact that the large piston (36) isformed as a hollow piston, by the fact that the small piston (228) ishollow throughout and is formed as a stepped piston with a section oflarger outside diameter and with a section of smaller outside diameter,by the fact that the small piston (228), with the section of largeroutside diameter, enters the pressure space (25) in a sealed-off mannerand, with the section of smaller outside diameter, enters the hollowlarge piston (36) in a sealed-off manner, and by the fact that the screwspindle (25) passing through the small piston (228) can be accommodatedby the cavity (186, 231) in the large piston (36).
 64. The drive deviceas claimed in claim 62 or 63, characterized by the fact that the smallpiston (228) is locked against rotation by the large piston (36) byintermeshing locking parts (232, 236).
 65. The drive device as claimedin one of claims 62 to 64, characterized by the fact that the spindlenut (234) is a separate part which is screwed to another part (233) ofthe small piston (228).
 66. The drive device as claimed in a precedingclaim, characterized by the fact that the large piston (36, 290) isformed as a hollow piston, by the fact that a screw spindle (25)arranged in an axially fixed position can be rotationally driven by theelectric motor (11), and this screw spindle (25) passes through a base(38) of the intermediate part (37, 287) of the hydraulic unit (12) andis accommodated by the cavity in the large piston (36, 290) and is inengagement with a spindle nut (253), by the fact that the small pistonis formed by a plurality of little pistons (256) which are arrangedoutside the axis of the hydraulic unit (12), are supported axially onthe spindle nut (253) and plunge into holes of the intermediate-partbase (38).
 67. The drive device as claimed in claim 66, characterized bythe fact that the pressure space (35) comprises an annular space whichis defined radially on the outside and inside by axial intermediate-partwalls (94, 257) and axially on the one side by the intermediate-partbase (38) and on the other side by an annular section (258), plungingbetween the intermediate-part walls (94, 257), of the large piston (36).68. The drive device as claimed in claim 66 or 67, characterized by thefact that the spindle nut (253) plunges into the central passage of theintermediate-part base (38).
 69. The drive device as claimed in apreceding claim, characterized by the fact that the pressure space (35)of the hydraulic unit (12) can be connected to a hydraulic accumulator(260, 280, 423), and by the fact that pressure fluid can be displacedfrom the pressure space (35) into the hydraulic accumulator (260, 280)as a function of the operating state, in particular as a function of thepressure in the pressure space (35) or as a function of travel.
 70. Thedrive device as claimed in claim 69, characterized by the fact that thehydraulic accumulator (260) is a piston accumulator and has anaccumulator piston (261) which is loaded by a spring (264) and which, ata certain pressure, is pressed against a stop against the force of thespring (264).
 71. The drive device as claimed in claim 69 or 70,characterized by the fact that a valve (281, 475) is arranged in thefluid connection between the hydraulic accumulator (280, 423) and thepressure space (35), with which valve (281, 475) the fluid connectioncan be shut off.
 72. The drive device as claimed in claim 71,characterized by the fact that the valve (281) can be actuatedelectrically and is operated at the same time as the release of anelectromagnetically actuable clutch (195).
 73. The drive device asclaimed in a preceding claim, characterized by the fact that the largepiston (36) is formed as a diaphragm piston with a diaphragm (290). 74.The drive device as claimed in claim 73, characterized by the fact thatthe diaphragm (290) is of elastic construction and at the same timeforms the coupling device with which the intermediate part (287) and thelarge piston (36) are coupled to one another in a fixed position for theregulating movement.
 75. The drive device as claimed in claim 73 or 74,characterized by the fact that the diaphragm (290) is fastened at anouter margin to the intermediate part (287) of the hydraulic unit (12)and is provided centrally for fastening to the part to be moved.
 76. Thedrive device as claimed in claim 73, 74 or 75, characterized by the factthat a radial gap, varying in its width, between the diaphragm piston(36) and the intermediate part (287) of the hydraulic unit (12) issealed off by two sealing diaphragms (294, 295) which are held tightlyon one another at a relatively large distance from the radial gap at aninner margin or an outer margin, and of which one sealing diaphragm(295), with its other margin, is fastened tightly to the intermediatepart (287) and the other sealing margin (294), with its other margin, isfastened tightly to the diaphragm piston (290).
 77. The drive device asclaimed in a preceding claim, characterized by the fact that the powertransmission means (12) is constructed so as to be double-acting, inwhich case at least the large piston (36) is constructed so as to bedouble-acting.
 78. The drive device as claimed in claim 77,characterized by the fact that the two pistons (334, 36) are formed assynchronous pistons.
 79. The drive device as claimed in claim 77 or 78,characterized by the fact that the large piston (36) has a cavity (332)in which the small piston (334), movable via a piston rod (340) emergingfrom the large piston (36), is located and which is divided by the smallpiston (334) into a first small sectional space (337) and a second smallsectional space (336), by the fact that the large piston (36) divides acavity of the intermediate part (317) of the hydraulic unit (12) into afirst large sectional space (321), which, with the first small sectionalspace (337), forms the first pressure space (35), and into a secondlarge sectional space (320), which, with the second small sectionalspace (336), forms the second pressure space (35), and by the fact that,as part of a pressure space (35), a fluid path (338, 339) runs between asmall sectional space (336, 337) and the corresponding large sectionalspace (320, 321) through the large piston (36) or the small piston, andthis fluid path (338, 339) is open at least for the power transmissionto come into effect.
 80. The drive device as claimed in one of claims 77to 79, characterized by the fact that the intermediate part (317) of thehydraulic unit (12) can be locked against a displacement relative to thefixed frame by friction grip with the fixed frame, and the friction gripcan be produced by hydraulically applying pressure to the onefriction-grip partner (92), and by the fact that the application ofpressure is effected in each case from the pressure space (35) underpressure, the other pressure space (35) being shut off toward thefriction-grip partner (92) acted upon.
 81. The drive device as claimedin one of claims 77 to 80, characterized by the fact that at least onespring (324, 461, 462) is supported between the large piston (36) andthe intermediate part (317, 437), and by the fact that the one part (36,317, 437) can be loaded in the direction of a center position relativeto the other part by the at least one spring (324, 461, 462).
 82. Thedrive device as claimed in one of claims 77 to 81, characterized by acoupling device (180, 195) arranged between the small piston (334) andthe large piston (36) or the intermediate part (437) and having a clutchpart (203, 457) which is loaded in the direction of a shoulder (342,456) of the small piston (334) by a spring (344, 459) supported on thesmall piston (334).
 83. The drive device as claimed in one of thepreceding claims, characterized by the fact that the one end of thescrew spindle (25) is mounted in a radial bearing (270) which, if aradial force exceeds a limit force, is radially adjustable relative to aguide bush (274) serving for the longitudinal guidance of the screwspindle (25).
 84. The drive device as claimed in a preceding claim,characterized by the fact that it serves to close and open the mold onan injection molding machine for plastics and a drive device (400) foractuating at least one ejector (408) is combined with it.
 85. The drivedevice as claimed in a preceding claim, characterized by the fact thatthe coupling device (180) between the drive element (28, 253) or thesmall piston (334), on the one hand, and the intermediate part (437) orthe large piston (36), on the other hand, is a hydraulic clutch (180)having a clutch space (426, 467) between the two parts that can becoupled to one another, in which case pressure fluid, during theregulating movement, is trapped in the clutch space (426, 467) betweenthe two parts coupled to one another and can be displaced from theclutch space (426, 467) for moving the two parts relative to oneanother, and by the fact that, for the regulating movement, the clutchspace (426, 467) can be connected to a high-pressure accumulator (425)via a directional control valve (428, 475).
 86. The drive device asclaimed in claim 85, characterized by the fact that, for moving the twoparts (28, 253, 36, 437), which can be coupled to one another, relativeto one another, the clutch space (426, 467) can be connected to alow-pressure accumulator (423) via the directional control valve (428).87. The drive device as claimed in claim 85 or 86, pressure fluidflowing over during a working cycle from the high-pressure hydraulicaccumulator (425) via the clutch space (426, 467) into a low-pressureaccumulator (423), characterized by the fact that the small piston (28,334) has a pump piston section (420, 458) which adjoins a displacementchamber (421, 466) and by the reciprocal movement of which pressuremedium can be drawn from the low-pressure accumulator (423) into thedisplacement chamber via a valve (422), in particular a check valve, andcan be displaced from the displacement chamber via a valve (424), inparticular a check valve, into the high-pressure accumulator (425). 88.The drive device as claimed in claim 87, characterized by a spill valve(429) arranged between the high-pressure accumulator (425) and thelow-pressure accumulator (423) and opening toward the low-pressureaccumulator (423).
 89. The drive device as claimed in a preceding claim,characterized by the fact that the power transmission means (12) isconstructed so as to be double-acting and has a double-acting largepiston (36) with a piston collar (319) adjoining a first large pressurechamber (321) and a second large pressure chamber (320), by the factthat the small piston (334) has a first piston section (457), adjoininga first small pressure chamber (466, 467) from which pressure fluid canbe displaced into the first large pressure chamber (321), and a secondpiston section (455) which is movable relative to the first pistonsection (457) and adjoins a second small pressure chamber (464), fromwhich pressure fluid can be displaced into the second large pressurechamber (320), by the fact that the second piston section (455) can becarried along by the drive element (25) by positive coupling, by thefact that the part (437) accommodating the small piston (334) has a stop(460) for the first piston section (457), from which stop (460) thefirst piston section (457), in the direction for reducing the firstsmall pressure chamber (466, 467), can be carried along by the driveelement (25) in a first direction, whereas in the opposite, seconddirection, after the first piston section (457) bears against the stop(460), the second piston section (455) can continue to be moved forreducing the second small pressure chamber (464).
 90. The drive deviceas claimed in claim 89, characterized by the fact that the drive element(25) passes through the first piston section (457), crosses a space(465) acted upon by atmosphere or low pressure, and then enters thesecond pressure chamber (455).
 91. The drive device as claimed in claim89 or 90, characterized by the fact that a spring (459) is secured inposition between the two piston sections (455, 457) of the small piston(334), this spring (459) loading the first piston section (457) in thesecond direction.